Control Techniques for Feral Hogs

GARY A. LITTAUER, District Supervisor, Texas Animal Damage Control Service,
Courthouse #19, Uvalde, Tx. 78801

Abstract: Methods of controlling feral hog damage are described. Literature on fence designsto exclude hogs indicates hog-proof fences must be net or diamond mesh wire with small (< 15 cm) wire spacings. Several designs of electric fences or electrifying existing fences are reported to be effective in excluding most hogs. Lethal techniques described include neck snares, cage or pen traps, hunting with dogs, and aerial hunting with helicopters. These techniques accounted for 55%, 14%, 6.3%, and 17%, respectively, of the hogs taken by the Texas Animal Damage Control Service during 1983-1992. An integrated approach to controlling feral hog damage is recommended.


Feral hogs (Sus scrofa) can cause significant damage to grain and vegetable crops in localized areas. They frequently learn to kill and eat lambs and kid goats and, to a lesser extent, prey on adult sheep and goats as well. Transmission of diseases such as brucellosis and pseudorabies to livestock and humans is also a concern among livestock producers and to animal and public health authorities (Texas Animal Health Commission 1992).

The consensus among ranchers and Texas Animal Damage Control Service (TADCS) personnel is that feral hog numbers are increasing in sheep and goat producing areas. This is supported by a nearly 10-fold increase in the take of feral hogs by the TADCS from 1983-1992 (TADCS files). Factors causing such an increase are the relatively high fecundity of feral hogs (Sweeney, et al. 1979; Baber and Coblentz 1986; Peine and Farmer 1990) and the increase in the availability of habitat where control efforts are not allowed due to sale of ranch properties to nonranching interests.

The tendency of feral hogs to cause damage and the threat of disease transmission have resulted in an increased interest in controlling their movements and populations. The purpose of this paper is to describe techniques and strategies for controlling feral hogs.

Exclusion

Fences

A number of fence designs have been described for controlling hog ingress into crop fields or lambing pastures. Nonelectric fences must be of net wire or diamond mesh construction with the spacing of vertical wires at about 15 cm (6 inches) or less to be pig-proof (Hone and Atkinson 1983, Tilley 1973). However, rectangular net wire in goat producing areas must have spacings of either < 10 cm (4 inches) or > 30 cm (12 inches) between vertical wires to keep goats from having their heads caught (R. Craddock, Ext. Sheep and Goat Specialist, Texas Agricultural Extension Service, pers. comm). In general, fences must be at least 91 cm (36 inches) tall and must be tightly stretched and/or buried beneath the ground at the bottom to be effective (Tilley 1973). Hog-proof fencing is difficult to achieve across terrain with dips and gullies and can increase costs substantially.

Electrifying existing net wire fences may be a less costly way to exclude hogs. Hone and Atkinson (1983) reported 4 different electrified fence designs that deterred nearly 94% of pigs from crossing in pen tests. All but one were of net wire construction with 30 cm (12 inch) spacing of the vertical wires (suitable for goat pastures) and an electrified stand-off wire 15 cm (4 inches) toward the pig side of the fence and 24 cm (9.5 inches) above ground. The pigs encounter the live wire first when trying to enter the pasture. The main fence is grounded to increase effectiveness.

The application of herbicides or other vegetation control techniques may be necessary along fencelines to prevent plant growth from grounding electric wires and/or to allow inspection and maintenance. Care must be taken to avoid spraying herbicides directly on wires as some formulations are corrosive and can result in rapid deterioration of the fence (Tilley 1973). Electric fences can require substantial amounts of maintenance to assure effectiveness and may not be practical in areas of rugged topography. Hog proof fencing is not economically feasible in much of the sheep and goat producing areas in Texas.

Lethal Techniques

Snares

Snares are the most important single tool of the TADCS for removing feral hogs in sheep and goat producing areas. Snare use accounted for 55% of the feral hogs removed by TADCS control efforts during 1983-1992.

The snare consists of a loop of steel cable attached to a secure object or a heavy drag and placed in a location so that the loop catches the animal as it passes through a small area. The snare has a sliding lock device that allows the loop to close but not open easily. A heavy swivel is used on the end of the cable that is attached to the anchor to minimize problems of twisting and breakage of the cable by the captured animal.

The TADCS primarily uses aircraft quality galvanized steel cable of 2.4 or 3.2 mm (3/32 or 1/8 inch) diameter for hog control. A number of suitable lock types are available from commercial sources. The best locks we have found, however, for the 3.2 mm cable are ones we make ourselves from 1.9 cm (3/4 inch) by 3.2 mm (1/8 inch) angle iron cut in 1.9 cm lengths and punched or drilled with 4 mm (5/32 inch) inch holes. Large hogs can sometimes straighten or even tear cables free from some commercially available locks.

Snares for taking feral hogs are mostly placed under fences in holes or “crawls” that hogs are using as evidenced by tracks or hair caught on the fence. Frequently, hogs push under a fence and bend the bottom wires up into a highly visible arc. Sometimes, if the fence is tightly stretched, it springs back into position after the hog pushes under it leaving little evidence that hogs are using the spot to cross. Closer observation shows the drag marks in the soil made by the fence stays and perhaps hair caught on the bottom wire. This type of evidence is easily missed by an inexperienced observer.

The swivel end of the snare is most often tied with a doubled or tripled length of tie wire to the bottom wire of the fence. The loop is suspended from the bottom wire of the fence with U-shaped wire clips or a single wrap of small gauge copper wire so that the loop pulls free easily when the animal passes through it. Sometimes a cable extension is used to attach the snare to one or several of the top wires which may be stronger than the bottom wire on some fences. Where fences are weak or when it is desirable to keep a productive crawl location from being torn up by captured hogs, a cable extension can be used to attach the snare to a large log, uprooted cedar stump, or similar weighted object which then serves as a drag.

In areas where the risk of capturing sheep, goats, calves, or other nontarget animals is low, snares can be set in trails used by hogs. A loop of 25-30 cm (10-12 inches) is effective and should be suspended about 18-20 cm (7-8 inches) off the ground to catch a 13.5 kg (30 lb.) or larger hog. Trail snares are attached by cable extensions to trees, drags, or steel stakes driven into the ground. Trail snares are infrequently used by the TADCS due to the hazard to livestock and deer.

Snares are of relatively low cost compared to other control techniques such as aerial hunting. Disadvantages are:

  1. Only one hog can be captured at a time at an active fence location. If a number of hogs are causing damage and using one fence hole to enter the damage area, it can take a considerable amount of time to stop the problem. Hunting with dogs or aerial hunting may be advised in those situations.
  2. They are inappropriate in situations where trail sets cannot be used and where the hogs live entirely within a pasture and do not pass under fences.
  3. Large hogs occasionally break snares.
  4. Nontarget animals are sometimes taken.

Cage Traps

Large cage or pen traps are often effective in taking feral hogs. Such traps accounted for about 14% of the hogs taken by the TADCS from 1983 through 1992. Although damage control efforts that use cage traps generally rely on them as a lethal method of control, they are also used to take hogs alive.

Cage traps come in a variety of designs. Taylor (1991) describes one design using a spring-loaded gate. Figure 1 shows a multiple catch design commonly used by the TADCS which consists of heavy gauge welded wire stock panels 3 m (10 feet) in length and 1.5 m (5 feet) high. Square steel tubing is welded to the perimeter of each panel to make it rigid. Four of these panels are set up in a suitable area and wired together at their ends to form a pen.

One of the panels is designed to accommodate an entrance gate which consists of a 74 cm (24 inch) wide by 91 cm (24-31 inch) tall rectangular hinged door with the hinge across the top of the gate. When closed, the gate rests at a 30 degree angle with the downward slope of the gate toward the center of the trap. The gate is propped up 46-51 cm (18-20 inches) with a stick so the first hog has a relatively unimpeded entry into the trap, but bumps the gate with its snout and causes it to fall. Once one hog is inside, others will generally push the gate up to enter, allowing multiple catches. A small rolled up piece of net wire fence wired to the underside of the gate provides a “cushion” for the hogs to encounter with their snouts when lifting the gate to enter the trap which enhances success.

In addition to the take-down panel trap, a portable design is used that is 1.2 X 2.4 m (4 X 8 feet) square and will fit on a utility trailer for transporting. This design is easier to move and set up but will not hold as many hogs as the larger panel style. Baits used for feral hogs generally consist of soured grain or carrion. Feral hogs prefer fermented corn mash over many other baits by feral hogs (Peine and Farmer 1990). Carrion seems to be more effective in cool than warm seasons and is less attractive to raccoons (Procyon lotor) than grain baits. Sheep and goat carcasses can usually be obtained from livestock shipping yards. Road-killed deer (Odocoileus sp., Hemionus sp.) can be a useful source of bait, but conservation officers should be consulted concerning legality.

Prebaiting the area and/or the trap with the gate wired open can enhance effectiveness. Letting the hogs become comfortable with feeding in and around the trap can increase the chance of multiple catches once the gate is set.

Turkey vultures (Cathartes aura) and black vultures (Coragyps atratus) sometimes drop into open-top traps baited with carrion and are unable to escape due to lack of take-off space. Using cage traps when the majority of turkey vultures have migrated south for the winter generally avoids this problem. Camouflaging traps with brush reduces their attractiveness to black vultures since they rely on sight rather than smell to locate food (Welty 1975). It is also believed to enhance capture success.

Occasionally, many hogs are caught at one time in a panel cage trap, and they are able to climb onto one another and reach the top of the panels to escape. To prevent this, a length of steel pipe can be wired to the top of the trap parallel to each panel and about 30 cm (1 foot) toward the center of the trap. This forms an effective barrier that keeps the hogs from climbing out.

An advantage of cage traps is that (1) a number of hogs can be captured at one time, and (2) they can take hogs that live entirely within a pasture (as opposed to snares). Disadvantages are (1) they are heavy and cumbersome to move and generally require 2 or more individuals to handle; (2) it is sometimes difficult to get hogs to enter the trap due to “trap shyness” and/or the availability of alternate food sources (i.e. acorn mast and crops or livestock that the hogs are already accustomed to eating); (3) traps are generally less effective in summer months.

Hunting with Dogs

Using dogs to trail and bay hogs is an age-old technique that is still used today. The technique consists of walking or riding horseback through hog inhabited areas while allowing the dogs to work and cast about for hog scent. Once a hog is started by the dogs, the chase is relatively short and the hog bays to defend itself. The hunter then catches up to the dogs by approaching the sound of their barking and kills the hog with a firearm.

Published studies evaluating this method indicate variable success (McIlroy and Saillard 1989). Undoubtedly, the experience of the hunter and dogs as well as that of the hogs being hunted are important factors in determining success.

A variety of dog breeds have been shown to be useful in hog hunting including several breeds of hounds (walker, blue tick, black and tan, and plott), and livestock working dogs such as blue lacy, pit bull (used primarily to catch and hold the hogs rather than trail), and even border collies. Dogs of mixed breed have also been used with success. Experienced hog hunters that use dogs have a wide range of opinions on what constitutes good hog dogs. Nevertheless, certain attributes that seem to characterize the more successful packs of hog dogs are:

  1. At least one dog should be a good scent trailer and experienced in trailing hogs. The dog preferably has the ability to detect and follow a trail that is several hours old, and will bark upon striking the trail.
  2. The dogs must be aggressive enough to consistently bay the hogs once they catch up to them. They must bark to let the hunter know the hogs are bayed.

An advantage of hunting with dogs is that many hogs can be taken in a relatively short time. The method can also be selective for taking individual depredating hogs. Where net wire fences surround the area to be hunted, snaring all exit holes just prior to hunting with dogs can increase hog take as hogs that escape from the dogs may then be caught in snares. Disadvantages are:

  1. It is often difficult to find and train good dogs. An experienced proven dog may cost $500 or more. A great deal of time and commitment are required to train dogs. The dogs must be hunted often to keep them in condition, and dogs that perform poorly must be culled. Dogs must be broken from chasing or attacking livestock, deer, and other nontarget animals.
  2. Dogs often are injured or even killed when baying hogs, particularly larger boars in dense cover. Veterinarian bills can be costly.
  3. In hot weather dogs can only hunt for a short while in the morning, or must be used at night. Many areas have terrain that is not conducive to night hunting. Rattlesnakes (Crotalus sp.) are more active on cool summer nights than during hot days and can pose a hazard to dogs and hunters.

Aerial Hunting

Aerial hunting involves shooting hogs from a fixed wing aircraft or helicopter. Helicopters are the primary aerial hunting tool used for hunting hogs in Texas. In most situations hogs inhabit brushy areas that are not suitable for fixed wing aircraft. Aerial hunting accounted for nearly 17% of the hogs taken by the TADCS from 1983 through 1992.

The technique requires an experienced pilot and a capable gunner. The preferred firearm is generally a 12 gauge autoloading shotgun. Preferred loads are 3″ magnum copper plated, buffered #4 buckshot. This load provides good penetration and knock-down capability, which is desirable for humane kills.

A ground crew of several individuals walking or riding horseback or on ATV’s or hunting with dogs through the area can enhance success.

Advantages of aerial hunting are (1) it is very selective since only target animals are taken, (2) a depredation or damage problem can be stopped in a short period of time, and (3) large numbers of hogs can be removed in a short period of time. Disadvantages are (1) high cost (e.g. helicopter costs can exceed $300 per hour), (2) in areas of heavy cover, effectiveness is limited since hogs can elude observation from the air, (3) it can be hazardous, particularly in areas of rugged topography, and (4) weather is a limiting factor.

Toxicants

No toxicants are currently registered for use against feral hogs in the United States. Compound 1080 (sodium monofluoroacetate) and warfarin have been used in Australia to control hogs (Hone and Pedersen 1980, McIlroy et al. 1989). If toxicant baiting methods were developed in the U.S., they could prove to be the most cost effective of all population control techniques. Researchers evaluating pig control methods in the Galapagos islands concluded that poisoning with hidden baits could have been 11 times cheaper than shooting and 80 times cheaper than live trapping in terms of cost per pig removed (Coblentz and Baber 1987).

Potential problems in the development and registration of toxicant methods for control of feral hogs in the U.S. include (1) nontarget hazards, both from the direct consumption of bait and from the secondary hazard to scavengers that feed on poisoned hog carcasses and vomitus, and (2) the cost of complying with data requirements of the U.S. Environmental Protection Agency. The use of antiemetic drugs to prevent vomiting by poisoned hogs (Rathore 1985) and selective baiting strategies such as using buried potatoes or other baits to take advantage of the rooting behavior of hogs (McIlroy 1983) might adequately reduce or eliminate nontarget hazards. Costs for the registration of a single chemical use could range from $500,000 to > $3,000,000 (E.W. Schafer, Registration Liaison, U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Animal Damage Control (USDA,APHIS,ADC), Denver Wildlife Research Center). Feral hog control ranked lowest in priority in a survey of State Directors in the ADC (Packham and Connolly 1992), lessening the chance that funds will be made available for research and development of toxicants for hog control.

Developmental Control Strategies

The use of feral hogs fitted with radio transmitters to betray the locations of groups of hogs (“Judas pigs”) to facilitate hunting success was suggested by Pech et al. 1992. The success of this technique depends on the formation and stability of groups which can vary substantially among seasons (Pech et al. 1992) and which probably also vary with the distribution of food and water sources. The “Judas Pig” concept is currently being evaluated in limited field trials in Texas to determine if aerial hunting success can be enhanced in sheep and goat producing areas.

Conclusions

Agricultural producers in need of hog control programs must consider the value of the crops or livestock prone to damage and weigh those values against the cost of control. Fencing may be too expensive in many instances to be cost effective. It may be the only solution, however, in situations where the hogs are raiding crops from adjacent properties where other control methods are not allowed. Since hogs are notorious at crossing even aggressive fence designs, producers should use an integrated approach to solving hog damage problems. This means a combination of methods, including lethal where necessary or desirable due to population management goals, should be considered.

Literature Cited

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Coblentz, B.E., and Baber, D.W. 1987. Biology and control of feral pigs on Isla Santiago, Galapagos, Ecuador. J. Appl. Ecol. 24:403-418.

Hone, J., and Atkinson, W. 1983. Evaluation of fencing to control feral pig movement. Aust. Wildl. Res. 10:499-505.

Hone, J., and Pedersen, H. 1980. Changes in a feral pig population after poisoning. Proc. Vert. Pest Conf. 9:176-182.

McIlroy, J.C. 1983. The sensitivity of Australian animals to 1080 poison. V. The sensitivity of feral pigs, Sus scrofa, to 1080 and its implications for poisoning campaigns. Aust. Wildl. Res. 10:139-148.

McIlroy, J.C., Braysher, M., and Saunders, G.R. 1989. The effectiveness of a warfarin poisoning campaign against feral pigs, Sus scrofa, in Namadgi National Park. Aust. Wildl. Res. 16:195-202.

McIlroy, J.C., and R. J. Saillard. 1989. The effect of hunting with dogs on the numbers and movements of feral pigs, Sus scrofa, and the subsequent success of poisoning exercises in Namadgi National Park, A.C.T. Aust. Wildl. Res. 16:353-363.

Packham, C.J., and Connolly, G. 1992. Control methods research priorities for animal damage control. Proc. Vert. Pest Conf. 15:12-16.

Pech, R.P., McIlroy, J.C., Clough, M.F., and Green, D.G. 1992. A microcomputer model for predicting the spread and control of foot and mouth disease in feral pigs. Proc. Vert. Pest Conf. 15:360-364.

Peine, J.D., and Farmer, J.A. 1990. Wild hog management program at Great Smoky Mountains National Park. Proc. Vert. Pest Conf. 14:221-227.

Rathore, A.K. 1985. Use of metoclopramide to prevent 1080-induced emesis in wild pigs. J. Wildl. Manage. 49:55-56.

Sweeney, J.M., Sweeney, J.R., and Provost, E.E. 1979. Reproductive biology of a feral hog population. J. Wildl. Manage. 43:555-559.

Taylor, R. 1991. The feral hog in Texas. Fed. Aid Rep. Ser. No. 28. TX Parks and Wildl. Dept. Austin, TX. 20 pp.

Texas Animal Health Commission. 1992. Regulations for trapping or moving feral (wild) swine. Brochure No. 92-77. TX Anim. Hlth. Comm. Austin, TX.

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Acknowledgments

I thank C. Baird and A.L. Cox for providing information on hunting with dogs. C. Baird also provided information on use of cage traps. I thank R. Beach for reviewing this manuscript.