Most landscape professionals are familiar with the discomfort and pain that venomous arthropods-ants, wasps, spiders, fleas, ticks, scorpions, etc.-can cause. However, their venom can cause more than mere pain. More human deaths in the United States are attributed to venomous arthropods than any other group of venomous animals, including snakes. Deaths caused by arthropod bites or stings represent only a tiny fraction of the millions of victims. However, a higher number-about 25,000 per year in the United States-have severe reactions.
Arthropods often live in close proximity to people and can be abundant, resulting in a high contact rate with people. The venomous pests I'll discuss in this article include those whose bites or stings can be severe and have frequent contact with people. The greatest risk is in the Southern part of the United States where venomous pests are most numerous in population and variety, and where longer seasons allow multiple generations and longer periods of activity. However, every part of the United States is home to at least some of these pests. Grounds-maintenance employees need to understand the biology and behavior of venomous pests. This is essential in developing a good avoidance and management program.
Many chemical treatments for these pests are within the normal scope of operations for landscape professionals. However, if you are unsure about what treatment to use, contact a county extension agent, licensed consultant or qualified pest-control operator for recommendations. But use good judgment: Some operations, such as controlling hornet nests, can be dangerous for inexperienced people.
Arthropods cause three types of envenomization (exposure to venom): piercing/biting, vesicating/urticating and stinging. Piercing/biting arthropods inject a toxin through their mouth parts. Vesicating/urticating arthropods release toxins on contact through venomous hairs (urticating) or small body openings (vesicating). Stinging arthropods inject a toxin through a stinger located on the posterior end of the abdomen.
Piercing/biting pests *Chiggers. These are the larvae of mites sometimes referred to as "red bugs" or "harvest mites." Their bite results in itching around the infected area. The larvae crawl up grass blades, weeds or other vegetation and attach themselves to a passing host (human or animal). One to six generations occur each year depending on the geographical region. Each generation takes 30 to 60 days to complete depending on temperatures.
Contact with chiggers usually occurs where tall grass grows at the edge of lawns, or in densely vegetated areas bordering lawns, playgrounds, parks or golf roughs. Mowing weeds and grasses and removing overgrown vegetation on a regular basis reduces chigger populations. In addition, residual miticides applied to freshly cut tall grass will penetrate to target areas to reduce or eliminate chigger populations.
For personal protection, you can use insect repellents. You can apply certain permethrin-based products to clothing for chigger control. You also can apply diethyl toluamide (DEET-formulatedin many retail insect repellents) to clothing or skin around the waist, ankles or other favorite chigger-feeding sites. Pants tucked into socks or boots provides some protection. People exposed to chiggers can take a hot soapy bath to help remove them. For temporary relief from itching, apply antiseptic or anesthetic ointments to infected areas.
*Fleas. The cat flea is the most common flea, and it attacks cats, dogs and humans. The adult female must seek out a host to obtain a meal of blood before she can produce eggs. The bite results in skin irritation. You generally can eliminate flea problems by treating the host animals (pets) and the home interior or yard where pets spend most of their time. Frequent cleaning of pet bedding helps reduce populations.
Focus outdoor treatments on areas frequented by pets, such as resting areas close to building foundations, under decks and porches, doghouses and kennels. Keeping turf mowed and thatch at a minimal level allows insecticides to penetrate target flea populations. If possible, control wild hosts (stray cats and dogs, raccoons, opossums, moles, etc.) that maintain a reservoir of fleas. Many of these animals feed on grubs and other soil insects. You can discourage them by controlling their food source with an approved soil insecticide.
*Ticks. Ticks may be a problem in tall grass, weeds and wooded or shrubby areas. They occur mainly in overgrown vegetation around yards, picnic areas and golf roughs. Seldom do they pose a problem in well-maintained areas. Ticks come in contact with their victims by climbing up vegetation to await a passing host. They tend to crawl upward and attach to their hosts in areas constricted by skin folds or clothing and often attach to the base of the scalp, waist, knee or armpit.
Tick bites are quite irritating, but most ticks you'll encounter do not carry disease. However, the genera Ixodes and Rickettsis may transmit the bacterial infections we know familarly as Lyme disease and Rocky Mountain spotted fever. If you find a tick on yourself, remove it promptly to reduce the chance of disease transmission. With tweezers, grasp the tick's head as close to the skin as possible and slowly and gently pull it away from skin until it detaches. Then wash the bite area with soap and water and apply an antiseptic. If disease symptoms occur within 3 weeks, see a doctor.
Reduce tick populations by cutting grass, weeds and overgrown vegetation. Eliminate hiding places for wild host animals. Several insecticides control ticks in outdoor vegetation. Treat thoroughly where tall grass and weeds occur around lawns, pathways, golf roughs, doghouses and ornamental plantings. Treat when you first start to notice ticks-generally in early spring.
Ticks normally do not infest well-kept, closely mown lawns. For personal protection, avoid walking through overgrown vegetation and use precautions and treatments as you would for chiggers.
*Spiders. The female black-widow spider, with its familiar red-hourglass marking (see photo, page 33) on the underside of its abdomen, is the most feared spider inhabiting outdoor areas. You typically find this pest in its web under stones, woodpiles, loose bark, storage buildings, barns, outhouses and water faucets. Most people contact spiders accidentally by trapping them against their body-spiders do not actively seek out people.
Manage spiders by frequently cleaning to remove them and their webs from buildings and outdoor living areas. Routine hose washing of potential spider habitats helps discourage spider buildup. Wear gloves and long-sleeved shirts when working in spider-infested areas. You can apply approved insecticides to buildings and infested areas. Spray cracks, corners, around windows, stairs, closets, etc., according to label instructions.
*Centipedes. During the day, these long multi-segmented arthropods generally hide under rocks, boards or bark and in crevices, basements, porches, patios and moist, protected areas. They become active at night to feed on prey such as small insects.
Centipedes have two powerful claws located on the lower part of their body immediately behind their heads, which they use to inject venom. Most species are not a threat to people. However, the bites of some of the larger species, when accidentally picked up, stepped on or trapped against the body, can be a hazard. To avoid them, wear shoes and protective gloves when moving rocks or debris from the ground. Some insecticides are registered for use on centipedes, and you may want to use them in heavily infested areas.
*Wheel bug. This pest gets its name from a distinctive cogwheel-like crest located on the top side of the thorax. People accidentally contact this insect when handling vegetation, boards, rocks or other objects. When attacking humans, this insect penetrates the skin with its proboscis ("beak") and injects a toxic fluid. Some bites can be quite painful.
To avoid contact, learn to identify the wheel bug. If you encounter one, do not handle it. Wear protective gloves while working in bushes and vegetation. Despite occasionally biting humans, this insect feeds on other insects and is beneficial. Thus, control is not recommended.
Urticating/vesicating arthropods *Blister beetles. The predacious larvae of blister beetles feed on other insects, especially grasshopper eggs. We generally encounter the striped and marginal blister beetles, though other species occur. The adult beetles may leave a clear, amber-colored fluid on human skin. Ruptured thin membranes on the insect's body secrete this fluid, a vesicating (blister-causing) agent called cantharidin. It doesn't take much pressure against the beetles' body to trigger fluid release.
Avoid contact with these beetles. If one lands on your skin, blow it off-don't crush it. Where high populations occur, use yellow light bulbs for outdoor lighting to reduce their attraction to lights. Chemical control is normally not practical because of the mobility and wide distribution of blister beetles.
*Caterpillars. The three species of caterpillars listed in the following sections have stinging hairs or spines. In each case, victims typically contact them by accidentally brushing against them when working among shrubs on which the caterpillars feed. If you encounter them, do not handle them. When working on infested shrubs, wear protective gloves, long-sleeved shirts and long pants. If an area is heavily infested, you can use one of the insecticides registered for leaf-feeding caterpillars.
*Io moth caterpillar. This rather large (2 to 3 inches) caterpillar is pale green with stripes of red or maroon over white running the length of the body. Green and black venomous spines are near the center of each body segment. These caterpillars feed on shrubbery in the spring and summer. When the victim's skin touches the spines, they break off in or on the skin, allowing the toxin to flow.
*Puss caterpillar. These caterpillars, sometimes incorrectly referred to as "asps," grow to 0.8 to 1.2 inches long. They are completely covered with hairs, resembling elongated tufts of cotton, varying in color from nearly white to dark brown or gray. The body hairs can penetrate human skin and toxin is transferred under the skin. Normally, natural enemies keep populations under control. *Saddleback caterpillar. This caterpillar is rather easy to identify. It has a green to brown slug-like body (0.8 to 1.2 inches long) and has a distinctive brown or purplish saddle-shaped marking on a green and white saddle blanket. It has stout spines along its sides and on its four tubercles (appendages arising from its body). These spines connect at their bases to poison glands. The caterpillars usually feed on shrubs during the summer and fall.
Stinging arthropods *Paper wasps, hornets and yellowjackets. These are common pests on golf courses and in landscapes. They are social insects that live in nests or colonies. Mated queens emerge in the spring and begin constructing nests in which they lay their first clutch of eggs. As the summer progresses, the nests enlarge and populations grow rapidly.
*Paper wasps. These wasps build umbrella-shaped nests attached to buildings, trees and shrubs by a single stalk (see photo, page 36). They are less aggressive than hornets or yellowjackets but will sting people if they disturb their nests. When they attack, they release an alarm pheromone, a chemical that alerts other wasps to swarm and defend their colony.
People maintaining ornamental shrubs or hedges should be cautious of paper-wasp nests. Examine shrubs before trimming and treat any nests present. You can use insecticides formulated as "wasp-and-hornet spray" for control. Although you can spray nests during the day, it is safer to treat them at night. When treating a nest, don't stand directly under it. Wasps drop immediately when sprayed and if you are standing directly under the nest, your chances of getting stung are high. After a few hours or a day, you can knock down the nest.
*Hornets. Hornets are more difficult to deal with than paper wasps. The more common species, the bald-faced hornet, is long (up to 0.75 inch) and black with white markings on its face, thorax and the posterior end of its abdomen. They build their nests in shrubs, trees, on overhangs of buildings and other structures. The nests are large, multi-combed, made of gray paper-like material and resemble a large football. Hornets are easy to disturb, and nests may contain hundreds of wasps.
Occasionally, it may be necessary to contact a professional pest-control operator to remove their nest because many times they are out of reach. Treat the nests only at night. Be sure to cover all parts of your body with clothes including face, hands, wrists and ankles, during treatment. Apply an aerosol-type wasp-and-hornet spray or dust to the single opening of the nest, usually at the bottom where wasps enter and exit. Be sure not to break the paper envelope of the nest, as this will cause wasps to scatter everywhere. Several days after treatment, you can remove the nest provided all the wasps are dead. If not, retreat.
*Yellowjackets. Yellowjackets can be even more aggressive than hornets when their nests are disturbed. They get their name from their distinctive black and yellow coloration. They usually build their nests underground in burrows or under rocks or landscape timbers. However, some build their nests in attics, sheds or other structures.
Yellowjackets scavenge for food outdoors around picnic areas, parks and similar sites. They are more of a problem in late summer and fall when the colonies increase in number. Maintenance people can reduce contact with this pest by practicing good sanitation, thus reducing their food sources. Empty and clean trash cans frequently and equip them with tight-fitting lids. When practical, locate trash cans and dumpsters away from where people congregate.
Yellowjackets are less active in their nests at night. Therefore, treat their nests with an insecticide after dark. Wear protective clothing and use indirect light if you need it. Don't shine light directly into the nest-this may startle or disturb them, and angry wasps tend to fly toward light. It may be necessary to call a professional pest-control operator if the nest is difficult to treat or reach.
*Cicada killers. These large wasps burrow into turf and produce a frightening, loud buzz that annoys people. They seldom sting unless hemmed up in close quarters and will not defend their solitary nest. However, if they do sting, it is painful. They prey on cicadas, for which they search in shrubs and trees in the spring and summer.
Although these insects are beneficial, their behavior may interfere with human activity. They prefer areas with sparse vegetation for nesting. Therefore, good cultural practices that promote thick turf discourage their burrowing. Placing mulch or bark chips under play structures instead of sand also discourages wasp nesting. Where large populations occur, a broadcast application of an approved insecticide may be necessary.
*Fire ants. This probably is the most problematic pest of landscape areas in the South. Fire ants produce unsightly mounds on lawns, playgrounds, golf courses and other landscape areas and can inflict painful stings on humans an d animals. The ants can sting repeatedly and aggressively defend their nests. Scratching stung areas may result in secondary infection and scarring. If you've been stung, place ice packs or antibiotic ointments on the infected area. If an allergic reaction occurs, seek medical attention immediately.
The key to control is to kill the queens, because they are the only ants capable of laying eggs. Some nests may have up to 150 queens per nest. Chemical control includes two tactics: treating individual mounds and broadcast treatments. The best approach for control is to use both tactics together.
When only a few mounds are present, mound treatments are more practical. You need only a small amount of insecticide compared to broadcast treatments. You can treat individual mounds with baits, contact insecticides or injectable materials. When applying a bait, sprinkle it around each undisturbed mound but not on top of the mound. When using contact mound drenches, pour the diluted insecticide on top of the undisturbed mound and about 2 feet around it, thoroughly soaking the mound. The amount of water you use depends on the size of the mounds. If you use granules or dust, cover mounds thoroughly, and, if the label instructs you to, water the granules into the undisturbed mound. Injectable products, often formulated as vapors or aerosols, may be more expensive and time-consuming to use but tend to give good results as mound treatments.
The best method of controlling fire ants over a large area with many mounds is by applying spring and fall broadcast applications of ant baits. With broadcast applications, it is not necessary to locate individual nests because foraging ants pick up the bait and carry it back to their nest. This method is effective and also controls mounds too small to see above the turf. You can make supplemental treatments with a contact insecticide applied to individual mounds that become established between bait applications.
Fire-ant control programs are most effective when every turf or grounds manager in the area treats for the ants. Thus, managers should take a team approach when implementing their fire-ant management program.
*Scorpions. These pests are flattened crab-like creatures with ten legs and a fleshy tail bearing a stinger (see photo, below). They normally live outdoors under boards, rocks, stones or other structures and vary in size from 1 to 4 inches long. Normally, scorpions live for 3 to 5 years. They feed on insects, other species of scorpions and sometimes even their own young.
Scorpions are primarily active at night, and they sting when provoked or disturbed. If you are stung, wash and disinfect the stung area. If the sting becomes persistently sore and swollen, see a medical doctor.
You can control scorpions mechanically (swatting or crushing). However, do not handle them. Wear gloves, shoes and clothing when working in a suspected infested area. Natural predators often provide good suppression of scorpions, but you can apply insecticides if necessary.
General precautions You can minimize the danger of being bitten or stung by venomous arthropods in several ways. Some are common-sense steps, such as not walking around in the yard in bare feet. Keep sweet items like ripe fruits and watermelons covered outdoors, because they attract bees and wasps. When bees and wasps are collecting nectar from flowers outside, avoid mowing and working in flowerbeds, if possible. If a venomous insect is near you, stand still. Brush it off if it attacks, but don't slap it to prevent a bite or sting. Implement chemical-control measures if these pests become numerous near heavily used areas. Finally, if you are attacked by a swarm of wasps, yellowjackets, hornets or bees, leave immediately using your arms and hands to protect your face.
Prompt action is necessary when anyone is bitten or stung. First of all, identify the pest. If possible, capture it and have it identified. If you suspect the victim is having an allergic reaction or has a history of hay fever, allergy or asthma, contact a medical doctor immediately.
Dr. J. Pat Harris is an extension entomologist at Mississippi State University (Decatur, Miss.).
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