Stinging or Venomous Insects and Related Pests

Millions of people in the United States are injured from venoms produced by insects and other arthropods each year. Of these injuries about 25,000 result in severe injuries and about 32 result in deaths (Table 1 ).

 

Venoms

Venomous insects and other arthropods produce venoms that can be classified as:

1. Venoms that produce blisters (vesicating toxins) (e.g., blister beetles, certain stinging caterpillars, millipedes).

2. Venoms that attack the central nervous system (neurotoxins) (e.g., black and brown widow spiders, bark scorpions, certain ticks, Hymenoptera, wheel bugs).

3. Venoms that destroy tissue (cytolytic and haemolytic) (e.g., Hymenoptera, fire ants, ground scorpions, mites, chiggers, wheel bugs, brown recluse spider).

4. Toxins that prevent blood from clotting (haemorrhagic) (e.g., lice, fleas, ticks, mites, true bugs, biting flies).

Allergic Reactions

Humans differ greatly in their reaction to arthropod venoms. Allergic reactions are often more important than the toxic effects of arthropod venoms. Of individuals who die from arthropod venoms, 96% had an allergic reaction. Allergic reactions to stings or bites are when something happens to a part of the body other than the immediately affected area. Allergic reactions are classified according to the severity:

1. Slight general reaction-inflammation, welts, itching, malaise and anxiety.

2. General reaction-a slight general reaction, plus 2 or more of the following symptoms: swelling, wheezing, abdominal pain, nausea or vomiting.

3. Severe general reaction-any of the above, plus 2 or more of the following: difficulty in breathing, difficulty in swallowing, hoarseness, confusion or feeling of impending disaster.

4. Shock reaction-any of the above, plus 2 or more of the following: cyanosis, fall in blood pressure, collapse, unconsciousness or incontinence.

Insect stings result in rapid progression of toxic effects. Of 208 deaths, 80% occurred less than one hour after being stung by Hymenoptera (bees, wasps, yellow jackets, or hornets). Spider bites, however, have a longer time interval between bites and death, with 89% of 54 victims dying more than 12 hours after being bitten. Statistics also reveal that of snakebite victim deaths, 17% died 1 to 12 hours after being bitten and 64% between 12 hours and 2 days.

What to Do

Insect stings require quick, prompt action.

1. The causative organism must be captured, saved and identified.

2. If a general allergic reaction is suspected, or the victim has a history of hayfever, allergy or asthma, a doctor should be contacted immediately.

3. Venom that is haemolytic, haemorrhagic or vessicating can cause marked swelling or discoloration at the sting or bite site. Keep victim warm and quiet until a physician is reached.

4. Venom that is neurotoxic can cause little or no swelling or discoloration at the sting or bite site. Apply ice to the site or immerse the affected part of body in ice water until a physician is reached.

5. Persons who have exhibited a severe allergic reaction in the past to arthropod venoms or have a history of asthma, hayfever or allergies should:
   • Undergo skin testing to determine hypersensitivity to arthropod venoms.

   • Carry identification or tags noting hypersensitivity.

   • Consider desensitization (immunization).

   • Carry an insect sting kit (available only with a physician's prescription).

Prevention of Stings

Several procedures can be used to minimize the danger of being stung by venomous arthropods.

1. Avoid mowing lawns or working with flowering ornamentals when bees and wasps are collecting nectar.

2. Don't walk barefooted in the yard.

3. Sweet items like soft drinks, ripened fruits and watermelons attract bees and wasps. Keep these items covered outdoors. Pick fruit as it ripens and dispose of rotten fruits.

Some Common Venomous Arthropods

Pertinent information on common venomous arthropods is in Table 2 .

 

Bees

Bees are often confused with wasps. Although closely related, they differ in many ways. Bees feed pollen and nectar to their young. They are beneficial insects that pollinate fruits, vegetables and many other plants. The most common bees are the honey bee (Figure 1 ), bumble bee , and carpenter bee. Bees are not commonly serious problems and usually require no control.

 

Figure 1. Honey bees.

When stung by a honey bee, scrape the bee's stinger out of the wound immediately. Be careful not to pull it out. If you do, you will force poison into the wound. If the stinger is not removed, the poison gland attached to the stinger will continue to pump poison into the wound for several minutes. Wasps and other bees do not leave a stinger and are capable of stinging many times. At certain times of the year (spring and early summer), honey bee colonies divide by swarming. Swarms are not usually a problem unless they land in an inconvenient spot or enter a building. A honey bee colony in a building must be removed after it has been killed to prevent problems from odors of decaying bees, honey and other pests.

 

Wasps

Hornets, yellow jackets , Polistes (Figure 2 ), mud daubers and the cicada killers are all wasps.

 

Figure 2. wasp.

They are generally considered to be beneficial because they attack and destroy many harmful insects found around homes and gardens. Hornets and yellow jackets kill such pests as house flies, blow flies and various caterpillars. Polistes are predators of corn earworms, armyworms and many other garden pests. Though beneficial, wasps also attack people. If disturbed, hornets, yellow jackets and Polistes will sting. Mud daubers and cicada killers usually are not as aggressive and will not sting unless touched or accidentally caught in clothing. If wasps build nests on houses or in bushes where children play or living activities are carried on, nest destruction or chemical control is necessary. Wasps can usually be identified by their nests and their location. Hornets, Polistes and mud daubers build nests above the ground. Hornets and Polistes nest in trees, shrubbery and under eaves. Mud daubers nest under eaves, porch roofs or similar sheltered areas. Yellow jackets usually build their nests in the ground, but sometimes build them above the ground. Cicada killers nest in the ground.

Hornets and yellow jackets build football-shaped paper-like nests . Polistes build paper-like nests that resemble a honeycomb. Mud daubers build clay or mud-cell nests. Cicada killers dig homes about one half inch across and pile the excavated soil around the opening.

Hornets, yellow jackets and Polistes are social insects and their colonies develop in a similar way. Adult females make up two castes: queen or fertile females which lay eggs; workers or sterile females which feed larvae and may lay eggs without mating if the queen dies during the season. In the fall, queens and males leave the nest and mate. The male dies and the surviving queens hibernate in cracks of rocks, under bark of trees, in buildings, or in the ground. In the spring the queen comes out of hibernation and builds a nest with a few shallow cells. An egg is laid in each cell and these hatch into worker larvae in 2 to 3 days. The queen feeds these larvae which develop in 12 to 18 days and spin cocoon caps over the cells and change into pupae. After the first brood emerges the queen resumes egg laying. The workers take charge of the nest, enlarging it and caring for the new larvae.

Mud daubers are solitary wasps. Each female constructs a clump of mud cells. There is no worker caste. In the spring, young adults come out of their nests and mate. The female then build mud-cell nests. After she completes the nest she captures about 20 spiders, paralyzing each with her sting as she catches it. Spiders are stored in the cell and she lays an egg on one of the spiders and caps the cell with clay. This is repeated until she has built one nest containing 6 to 20 cells. She may then build other nests in other locations. Once a nest is finished, she leaves it and never returns. The larvae hatch from the eggs and feed on the paralyzed spiders. Complete development takes place in the cell. One to three generations can develop in a year.

The cicada killer is also a solitary wasp. Its habits are similar to the mud dauber except it constructs its cells in the soil and provisions the cells with cicadas.

When a wasp stings it injects a venomous fluid under the skin. The venom causes a painful swelling that may last several days. In some cases a wasp sting may cause severe illness or even death.

Scorpions

Scorpions (Figure 3 ) are flattened, crab-like animals having ten legs and a flesh tail, ending in an enlarged upturned tip which bears a stinger. They vary in size from one to four inches long. They normally live outdoors, though they will invade homes and buildings. Scorpions will sting, but usually only when provoked or disturbed. Scorpion venom is a neurotoxin, but the dose injected usually is insufficient to prove fatal to an adult human. None of the several species of scorpions which occur in Florida is capable of inflicting a lethal sting; however, the site of the sting may be sore and swollen for some time.

 

Figure 3. Scorpion.

Scorpions are most active at night. They hide under boards, rubbish, or similar debris which provide shelter and protection. Places commonly infested in a home are under the house or in the attic. They feed on insects, spiders, or similar small animal life.

Scorpions have a long life cycle, lasting three to five years. Males and females go through a courtship ritual prior to mating. Scorpions do not lay eggs and the young are born alive. After birth the young scorpions climb on the back of the mother and remain there until after their first molt. Scorpions are cannibalistic and will readily eat their own species. Females will often eat their own young.

 

Spiders

Almost all spiders in Florida are harmless to man. Most species do not bite unless provoked to attack. The widow spiders, primarily the brown widow , the southern black widow (Figure 4 ) and the northern black widow, are the most frequently found venomous spiders.

 

Figure 4. Brown Recluse spider.

The brown widow is established pretty much throughout the Florida peninsula. It is most common on, but not restricted to, buildings. They are also found on bridges and fences as well. The egg sac looks like an old naval mine or a sandspur seed. The spiders are extremely timid; the only bites reported have resulted from a spider being accidentally trapped against the victim's body. They reproduce rapidly, and one female can produce up to 18 egg sacs. Once encountered, a spider is indicative of a widespread population which is extremely difficult, if not impossible given available control methods, to eradicate.

The brown recluse spider is not considered to be established in Florida although physicians have diagnosed its bites on patients.

 

Fire Ants

Fire ants ( Figure 5) look like ordinary house ants; however, they are an aggressive ant capable of inflicting a painful sting. The colony of imported fire ants is a mound sometimes 3 feet across.

 

Figure 5. Fire ant.

Wheel Bug

The wheel bug (Figure 6 ) is a predacious bug with a cog-like crest on its thorax. They feed on insects; however, humans are bitten by accidental contact. The bug penetrates the skin with its beak and injects a salivary fluid used to kill its prey. The fluid causes an immediate intense pain which lasts 3-6 hours. The best way to prevent wheel bug bites is to avoid the insect.

 

Figure 6. Wheel bug.

Blister Beetles

Blister beetles (Figure 7 ) are narrow beetles with a neck which is slenderer than the head and wings. Adult beetles can release a fluid which causes blisters on human skin. The larvae of blister beetles are harmless to man and are predaceous on other insects. The adult beetles feed on foliage, and persons often come into contact when moving through infested vegetation. The only suitable control of blister beetles is avoidance of individual beetles or chemical application to crop plants. It is necessary to check recommendations for the crop to determine the chemical to be used.

 

Figure 7. Blister beetle.

Stinging Caterpillars

Stinging caterpillars frequently found in Florida are the puss caterpillar, saddleback caterpillar, IO moth caterpillar, and the hag moth caterpillar. These caterpillars feed on vegetation and have spines which can break off in the skin. When the spines break, a toxin flows from the spines onto the skin, causing a burning sensation.

When working in an infested area, wear protective clothing.

 

Saddleback Caterpillar

This is a very unusual and striking insect (Figure 8 ) . It is brown with a green back and flanks on which is a conspicuous, brown, oval-shaped central area usually bordered with white. The brown spot gives the appearance of a saddle and the green area appears to be a saddle blanket; hence, the common name. It may exceed an inch in length and is stout bodied. The primary nettling hairs are borne on the back of paired fleshy protuberances toward the front and hind ends of the body. There is also a row of smaller stinging organs on each side. The saddleback caterpillar feeds on many plants including hibiscus and palms, and appears to show little host preference.

 

Figure 8. Saddleback caterpillar.

Puss Caterpillar

It is a convex, stout bodied larva, almost 1" long when mature and completely covered with gray to brown hairs. Under the soft hairs are stiff spines that are attached to poison glands. When touched, these poisonous spines break off in the skin and cause severe pain. Puss caterpillars ( Figure 9 ) feed on a variety of broadleaf trees and shrubs, but prefer oaks and citrus. In Florida, there appear to be two generations per year, one in spring and the other in the fall. Natural enemies keep these caterpillars at low numbers during most years; however, they periodically become numerous.

 

Figure 9. Puss caterpillar.

Hag Moth Caterpillar

This caterpillar is light to dark brown in color. It has nine pairs of variable length lateral processes that bear the stinging hairs. These processes are curved and twisted and likened by some to the disheveled hair of a hag, for which it is aptly names. The hag moth caterpillar is found on various forest trees and ornamental shrubs, but is not as common as the other stinging species.

 

IO Moth Caterpillar

This is a pale green caterpillar ( Figure 10 ) with yellow and red stripes. It often exceeds 2" in length and is fairly stout bodied. The nettling organs are borne on fleshy tubercles, and the spines are usually yellow with black tips. IO moth caterpillars feed on a wide range of plants; however ixora and roses are favorite hosts.

 

Figure 10. Io moth caterpillar.

Velvet Ant

Velvet ants (Figure 11 ) belong to a large family (Mutillidae), and look like wingless, ant-like wasps. The females are solitary with an efficient, large stinger. Most species are parasitic on solitary bees and wasp species.

 

Figure 11. Velvet ant.

Humans are usually stung by velvet ants when the female is accidentally stepped on with bare feet or trapped against the body in clothing or bedding. Since the velvet ant is solitary and roaming, control is difficult.

Tables

Table 1. Deaths from Venomous Pests (from Parrish AJMS, 1963)

Table 2. Summary of Important Stinging Arthropods.