[Stinging Insects] Not the Usual Suspects

Oftentimes when a service technician visits a residential home for a termite job or an indoor or outdoor standard application for structural pests, the homeowner will ask questions about “some other bug” in the backyard or in the structure itself. And, oftentimes the first question is “Can it bite?” or “Can it sting?” or “Will it hurt me if I accidentally run into one of these critters?” This article focuses on a brief review of the biology and behavior of three lesser-known stinging pests that pest management professionals may run into in urban environments that could potentially give their clients a scare.

The bottom line, as you may already know, is that most of the insects lurking around our homes are indeed harmless to humans, at least from the standpoint of bites and stings. And, of course, after having made that statement there are a few exceptions. The biggest exception is the stinging Hymenoptera — that large group of black/white/yellow creatures commonly known as bees, wasps and hornets. These pests bring terror to many individuals in the home and outdoor setting, and rightfully for those that may be pre-disposed to severe allergic reactions to bee stings.

Another problematic stinging pest is the red imported fire ant, which has received much attention throughout the years for its nasty sting and the resulting welt that it can cause. Then, of course, you have dust mites and German cockroaches, which have been associated with allergic reactions and asthma in the young and old. And, last but not least, the relentless buzzing mosquitoes that sometimes ruin our backyard picnics, pack an irritating itchy bite, and now, in recent years, have become a national concern because they can transmit West Nile virus (WNV), a potentially deadly disease. 

But beyond these critters, for which so much has been written and published, the vast multitudes of “creepy crawly bugs” in the home and backyard environments are harmless...well, for the most part at least.

IT’S WORTH REPEATING. As I write in almost all of my articles, the better rounded your technician is as an entomologist, the better he/she will be able to do their direct job, and the more professional they will project themselves to the client. It’s for these reasons that it is important they be able to provide information on those secondary entomology questions about “What bug is this?”; “Do I have to worry about this one?”; “Can these things bite my children?”; or any other number of questions that always seem to pop-up.

If you can provide some guidance when these questions arise, along with the already outstanding treatment you may have performed, you and your technicians likely will have earned the loyalty of these particular customers.

So, in the spirit of continually increasing entomological knowledge, let’s review some basic biology about a few “harmful insects” that we don’t tend to run across often, but that might pop-up from time to time, and pose a real or perceived threat to the homeowner.

BLISTER BEETLES. Blister beetles reside in the taxonomic family Meloidae, which contains about 2,500 different species. These beetles are found throughout the entire United States with the heaviest populations west of the Mississippi River. Blister beetles vary in size and shape, but can be recognized by the first portion of the thorax, just behind the head, which is narrower than either the head or first pair of wings. Also, the first pair of wings are soft and flexible.

Adult beetles are phytophagous (plant feeding), feeding especially on those in the families Amaranthaceae, Compositae, Leguminosae, and Solanaceae. Most adults consume floral parts, but some may eat leaves as well. A few adults are nocturnal, but most are active during the day or show no real preference for being active in the day or at night. The adults of most common blister beetle species are brightly colored and thus quite noticeable in a backyard setting.

As is the case with all beetles, they do go through complete metamorphosis; however, except for the first instar larvae (called triungulins) which can be seen frequenting flowers or clinging to adult bees, larval blister beetles are seldom seen. Larval blister beetles are specialized predators. They enter the nests of wild bees or other social insects, where they consume immobilized larvae and the provisions (food) that adult nest keepers have left for their young.

Blister beetles receive their common name due to the fact that their blood or hemolymph is capable of producing a rather impressive raised blistering of human skin — a very interesting response of the adult stage of this particular insect. The compound that causes the blisters is cantharidin. You might guess that cantharadin serves as a defense mechanism utilized by adult beetles if they are attacked; however, there is little evidence in the literature to support this theory.

In some species of blister beetles, females receive large quantities of cantharidin from males during copulation. The females incorporate this material in a coating applied to the eggs. Cantharidin is an odorless compound in the chemical class known as terpenes. This special chemical is rather specific to blister beetles.

Cantharidin itself is a very interesting chemical compound. Used in the form of dried, crushed bodies of adult blister beetles, it was once employed extensively in human and veterinary medicine, primarily as an irritant. Whether taken internally or absorbed through the skin, cantharidin is highly toxic to mammals. Horse owners should be particularly aware of the danger of blister beetles. Horses may ingest cantharidin from consuming hay that had dead beetles in it (the cantharidin can remain active in dead blister beetle bodies).

If you encounter a client that has horses or other livestock and are concerned about blister beetles, have them contact their local cooperative extension service entomologist for more detailed veterinary information. Also, there is extensive literature dealing with the reputed properties of cantharidin as an aphrodisiac, the best known of which is with the Eurasian Spanish fly, Lytta vesicatoria (Linnaeus). Numerous reports of human poisonings, both accidental and deliberate, have been recorded.

The blister beetle is capable of exuding blood from the body when an adult beetle is pressed, rubbed or otherwise disturbed. Blisters most commonly will occur on the neck and arms, as the result of exposure to adult beetles attracted to outdoor lights at night. Interestingly, general handling of adult beetles seldom results in blistering unless the exuded blood comes into contact with the relatively thin skin between the fingers or other parts of the body where thin skin membranes occur. The beetle only exhibits this response when pressure is applied to its body. Usually, medical treatment is not required unless the blistering appears to be extensive but, as always is the case with arthropod encounters, there are those rare instance when the blistering is severe enough to warrant medical attention. In these situations the best advice to  give is, “if you are not sure, it’s better to be safe rather than sorry.” In most instances of accidental encounters with blister beetles, the blisters soon diminished on their own.

VELVET ANTS. Velvet ants, which are not really ants at all, but solitary female wasps, belong to the taxonomic family Mutillidae. Velvet ants occur worldwide, with a total of about 5,000 species (400 in North America), of which most occur in the tropics. They are especially common in arid, sandy, desert areas, with most of the over 400 North American species found in California, Arizona, Texas, New Mexico, and adjacent parts of Mexico, with others found in generally sandy regions across the U.S. 

They are particularly prevalent where ground-nesting stinging pests, such as wasps, occur, and for good reason — velvet ants parasitize other wasp and bee nests to provide food for their young. Females attack the nest and actually lay eggs inside of the larvae and/or pupae of the invaded nest. When the velvet ant larvae hatch they are already surround by food! The young larvae will consume the host in which they hatched from.

Many species are nocturnal, which permits them to avoid the often hot, deadly conditions of the desert sun. Velvet ants get their name because their wingless body has the appearance of an ant, and the body often is covered with sometimes quite colorful shades of red and orange dense hairs. 

Males, in comparison, are larger and winged, though rarely seen. Female velvet ants — the ones that can sting you — vary from ¼ inch to 1 inch (25 millimeters) in length. Along the body is a covering of dense hair. Another interesting identifying feature of the velvet ant is that females will make a squeaking noise when captured and either pressed or squeezed. If you get close enough in contact with a velvet ant to hear this you may be closer than you want! However, if your curiosity gets the best of you, grab them with a pair of leather gloves or a piece of cloth thick enough to prevent you from being stung. Tweezers or forceps also will work well. 

In most cases, velvet ants do not reach pest status, though occasionally they do invade residences, daycares or schools in large numbers. When undisturbed they are not aggressive; however, if bothered, they are quite capable of inflicting a painful sting. The sting of a velvet ant is claimed to be one of the most painful of all insect stings. This is likely why in some parts of the country certain species of highly visible velvet ants have a common name of “cow killers,” supposedly because their sting is powerful enough to kill a cow! While this of course is not true, their sting is nevertheless usually very painful to humans. Throughout the United States the most common velvet ant species that typically make their way into the backyard environment are cow killer ants (Dasymutilla occidentalis) and red velvet ants (Dasymusilla magnifica). While these are the most common, it is a good idea to make certain of your ID before you pass on any information to a homeowner. As always, if you are uncertain, get a second opinion from a taxonomist.

Velvet ants are usually solitary, and thus no control measures are usually required.  However, if the wasp population increases to very high numbers and the sting incidence rises significantly then pest control measures may be taken. Commercial bee and wasp sprays will effectively kill this insect, but will also impact beneficial insects.

CICADA KILLERS. Cicada killers are large wasps, approximately two inches in length.  When in flight, in comparison to the other “usual suspects,” stinging Hymenoptera (bees, wasps, hornets, etc.), they appear quite impressive and will instill fear in most anyone who does not know that, despite their size and daunting appearance, they very rarely sting unless directly disturbed. I have, however personally experienced situations where male wasps will literally dive-bomb people as they walk by (golfers!) in an effort to “protect” their territory. In these situations, the fast and tactical flight of these large wasps can indeed be unsettling. I’ve observed individuals on golf courses swatting at them with their golf-clubs.

Cicada killers generally occur throughout the eastern United States, but only east of the Rocky Mountains. Only one species is common in the western U.S., the western cicada killer. Adult cicada killers tend to be a nuisance when they occur in late June or July. During this time they are most likely encountered visiting flowers or digging burrows in sandy or light soil. Golfers in the eastern U.S. may see large numbers of cicada killers in sand traps where they are not kept in check. Cicada killers have large amber-colored wings and their body is usually black or dark brown with various patterns of colorful markings, usually yellow, on the abdomen.

Like many ground-nesting Hymenoptera, cicada killers nest in the ground and provision their nests with insects that they hunt and kill. Any guesses on what the cicada killers feed their young? Yep, you guessed it, cicadas! If you have been fortunate enough to see this spectacle it is indeed quite impressive. The hunting wasp most often attacks and kills the cicada either in flight or up in a tree with enough elevation that will allow the wasp to take-off and fly back to the nest. Imagine trying to get a plane off the ground if it is slightly overloaded…this is what the wasp has to face! The cicadas that are captured weigh quite a bit more than the wasp themselves.

I’ve seen them jump out of a tree, heading for the ground fast with a big cicada in their grasp thinking they were going to crash-land, only to see them pull up at the last second, regain their composure, and make it to the nest with dinner. As in many insect species, the males appear as adults first, and mating takes place when adult females emerge from the soil. After mating, females select a site and begin digging a burrow. Favorite sites are embankments, under sidewalks and roadsides. Commonly, well groomed lawns tend to be a favorite site and this is where the cicada killer can become a nuisance.

Cicada killers are solitary wasps, but can occur in such numbers that they disturb lawns with their burrows. They WILL sting if bothered, but as mentioned before, this is usually not the case. For this reason, like the other insects mentioned in this article, they are only considered a minor or nuisance pest in the backyard setting. Usually it is not necessary to control cicada killer wasps unless their presence becomes a nuisance or severe concern to the homeowner. This most often occurs in high-traffic homes or outdoor public places like golf courses, swimming pools, entrances and exits of public buildings where there are plants or, of course, certain backyards that seem to be attractive to cicada killers because of the presence of prime nesting sites.

If a client has a particular situation where there are so many wasps around and there is a concern for treatment, many insecticides are available for wasp control. If control is necessary, follow the standard procedure for locating nests. During the day observe flight patterns of wasps, but return in the evening or very early morning hours when wasps are still in their nests due to the cool temperatures.

CONCLUSION. It is nearly impossible to identify every bug in the backyard setting, especially when someone is trying to describe a particular critter to you without a specimen or example.
Often, people will exaggerate the size or ferocity of pests, especially those that are perceived to be harmful e.g. stinging/biting insects. Remember, most often people inquire about something because they are concerned or scared they will receive a bite or be attacked by the critter in question.
If you are certain of the pest identification then you can offer information or suggestions for how to deal with the situation. However, always remember the first rule of any sound pest control strategy — properly ID the pest. If you are uncertain about a pest that someone is trying to describe, it is always better to try to find a specimen to ID, and offer that you will get back to them once you have made a proper ID.
Gather additional reference materials  about these fascinating creatures and share this information with your clients.

The author is a Racine, Wis., entomologist.