Wednesday, September 30, 2009

Indoor Insects of Autumn (part 2 of 4)

This is the second in a four-part series of entries addressing insects frequently seen indoors at this time of year when they seek shelter for hibernation during the colder months. This entry will introduce boxelder bugs in the genus Boisea.

At this time of year, people often encounter boxelder bugs in great numbers on trees, shrubs, or all too frequently on the exterior of their home. These insects go through simple or “incomplete” metamorphosis, and the nymphs are becoming adults just before cold temperatures set in. The winged adults are thus able to disperse to, and congregate in, sheltered niches insulated from the brutal winter weather.

There are two species of boxelder bugs in North America. East of the Rocky Mountains one finds the eastern boxelder bug, Boisea trivittata. West of the Continental Divide ranges the western boxelder bug, Boisea rubrolineata. Both species were formerly placed in the genus Leptocoris, and many older references used that name. They belong to the family Rhopalidae, collectively known as “scentless plant bugs,” owing to the usual lack of defensive scent glands like those possessed by other true bugs such as leaf-footed bugs (Coreidae) and stink bugs (Pentatomidae).

The bold red and gray color pattern of boxelder bugs suggests that they must have some form of defense against predators that they are advertising through those bright aposematic colors. Indeed, the eastern boxelder bug is known to produce compounds known as monoterpene hydrocarbons that have been shown to deter predation by green anole lizards (source at PubMed).

Boxelder bugs mostly constitute a cosmetic nuisance to homeowners, and they can be easily excluded from the interior of a residence. Make sure that the weatherstripping on doors reaches the floor, and mend any holes in the window screens. Do be careful of bringing the bugs in accidentally, as the stack of firewood out back makes a convenient cozy shelter for the hibernating masses, too.

Come next spring the boxelder bugs will disperse again to their favorite host plants. Despite their large numbers, they cause remarkably little damage as they feed on the seeds of boxelder, maple, and other trees. So, marvel at this spectacle of abundance and be tolerant. Maybe your neighbors will learn from your example as well.

Monday, September 28, 2009

Indoor Insects of Autumn (part 1 of 4)

This is the first in a four-part series of entries addressing insects frequently seen indoors at this time of year when they seek shelter for hibernation during the colder months. This entry will introduce the “western conifer seed bug,” Leptoglossus occidentalis.

Western conifer seed bugs, despite their common name, now occur over the entire northern half of the United States and adjacent southern Canada. They were initially a truly western species, but have since spread eastward. They were first recorded in Connecticut in 1985, for example.

These insects, members of the “leaf-footed bug” family Coreidae, are frequently mistaken for “kissing bugs,” blood-feeding assassin bugs in the genus Triatoma in the family Reduviidae. Conifer seed bugs are not the least bit dangerous, however, feeding on the seeds and developing cones of pines and other conifers. The long hind legs of these insects, with the slightly flared “bell-bottoms” appearance of their “ankles,” are a good field mark to look for in trying to identify these true bugs.

The western conifer seed bug is a fairly large, conspicuous insect roughly twenty millimeters long, and it flies with a loud, droning sound that makes it intimidating and unwelcome as an indoor guest. Furthermore, they are equipped with a pair of scent glands on the underside of the thorax. The bugs don’t hesitate to deploy their defense when molested, emitting a permeating pungent odor that deters all but the most determined predators.

Leaf-footed bugs are not without their enemies, though, chief among them being tachinid flies in the genus Trichopoda. The female fly lays at least one white, dome-shaped egg atop its host where it cannot be easily wiped off. The egg is in fact firmly adhered to the bug’s exoskeleton. Adult insects are doomed when the fly larva hatches and bores into its host’s body where it lives as an internal parasite. Immature bugs (nymphs) may occasionally escape the fly’s assault if they molt the exoskeleton before the egg hatches, though the bugs cannot molt at will, only when growth demands it.

Human beings can best deal with the western conifer seed bug by excluding them from their homes. This means repairing worn weatherstripping on doors, fixing holes in window screens, and blocking off other openings where the insects might enter, such as where plumbing and electrical conduits enter or exit the residence. Should one of the bugs still make an appearance, simply usher it gently into a container and take it outdoors. Normally, these bugs hibernate in snug, natural places such as under bark on logs, in woodpiles, rodent nests, and similar niches.

Thursday, September 17, 2009

Ambush Bugs

Goldenrod has been flowering for several weeks now here in western Massachusetts, as it has been over most of North America. The blooms attract an incredible number of bees, wasps, flies, moths, and butterflies that come for the nectar, but one other insect stakes out goldenrod to make a meal of those other visitors.

Ambush bugs, once placed in their own family Phymatidae, are squat, diamond-shaped insects now considered members of the Reduviidae, collectively known as “assassin bugs.” Fortunately, the only thing ambush bugs assassinate is other insects.

Colored in shades of yellow or cream with darker markings, ambush bugs are well-concealed among the buds and blossoms of a variety of flora. Often the only indication of an ambush bug’s presence is its prey: another insect posed motionless in an awkward position among the petals of a flower.

Ambush bugs seize their prey with amazing speed and strength. The entire adult insect is only about ten millimeters in length, but what they lack in size they make up for in muscle power. Their front legs are “raptorial,” heavily modified like a praying mantis for grabbing and holding a victim. The femur is heavy and almost club-like, while the tibia is blade-like. The two leg segments fold against each other like a jack-knife against its handle.

The attack is so forceful as to be an audible “snap.” Sometimes the bug literally bites off more than it can chew. I once saw an ambush bug attack a hovering leafcutter bee. The startled, retreating bee literally yanked its attacker off the flower and the bug was forced to abandon its effort and fly off to another flower to try its luck again.

While the bug’s grip is so strong that it can often subdue a victim with only one front leg, it is the bug’s bite that ultimately dooms its prey. Beak-like mouthparts deliver saliva containing paralytic compounds and enzymes that pre-digest the meal from the inside out. The ambush bug then sucks up the liquefied contents, leaving the prey insect as an empty exoskeleton.

Female ambush bugs are larger and heavier than the males, and able to snatch larger prey items. This fact has not been lost on the smaller sex, and males will ride piggy-back atop females, sharing in the female’s successful kills. Such couples may or may not end up as a mating pair, and given the male gender’s freeloading tendencies, it seems a wonder they reproduce at all.

It is not just another ambush bug that might share in the spoils, though. Tiny flies of the family Machiidae will congregate like vultures at the scene of the crime, lapping up any tasty liquids oozing from the deceased.

Our most common and widespread North American ambush bugs are in the genus Phymata, of which there are at least seventeen species. Look (carefully) on almost any flower at this time of year and you may be surprised to find one of them lurking there.

Saturday, September 12, 2009

Cicada shells

Almost every summer I receive several questions about strange bugs sitting motionless on fence posts, tree trunks, and other upright objects. I thought I would do an entry here to explain the mystery.

The descriptions of the creature that people give to me vary from a “cross between a crayfish and a beetle,” to “gnome-like,” and all mention the large claws on the “front end.” No one has ever seen anything like it, and it is no wonder. Normally, the creature they are seeing lives fairly deep underground.

I have taken to calling these bugs “former insects,” since the objects being seen are not entire insects but the cast exoskeletons (“skins”) of cicadas, family Cicadidae. Scientists call these shed skins “exuviae,” all that remains behind when the insect molts from the nymph stage into an adult. Dragonflies, damselflies, stoneflies, and mayflies also leave behind these ghostly but tangible shadows of their former selves.

The average person rarely sees an animated version of a cicada nymph because the mature nymphs emerge from the soil at night, climbing the nearest vertical surface, and then splitting the exoskeleton down the middle of the back to allow the escape of the wet, soft adult under the cover of darkness. The fresh, pale adults are extremely vulnerable, but their principle predators are diurnal, so they avoid instant death by coming out at night. Cicadas are large insects, so they can be quite conspicuous under the best of cryptic circumstances.

An adult "annual" cicada, Neotibicen sp.

Most people in eastern North America see the shells of “annual” or “dog day” cicadas in the genus Tibicen. They then hear the loud “songs” of the adult male cicadas, not often seeing the insect that makes such a racket. Despite the name, annual cicadas still take a long time to grow up. They live a subterranean existence as nymphs, sucking the sap from tree roots for at least five to seven years. The generations are staggered, though, so some adults emerge every summer. This is in contrast to the synchronous broods (populations) of the periodical cicads or “17-year locusts” that emerge en masse in the late spring or early summer every 13 or 17 years, depending on the latitude of the population.

I like to get questions about things like cicada exuviae. It shows that people are observant and curious, two qualities I really admire in my own species

Antifreeze and Rancid Snails

I should probably issue an advisory with this entry. I thought about including images, but they would be too graphic even for mature audiences. Suffice it to say that science is often (maybe even usually) a dirty, toxic business. I learned that in a convincing fashion over the last two weeks or so while I was processing raw pitfall trap samples.

You may recall that when I first began work here at the University of Massachusetts I was sorting pitfall trap samples from the 2008 field season. This year’s traps were even greater in number since the students sampled two watersheds instead of one. Last year’s samples had already been placed in alcohol, and were about as “clean” as one could expect. My task over the past couple weeks was to render this year’s specimens workable.

Scientists using pitfall traps face several challenges. First, you need to be able to kill the trapped animals quickly, before they can maul each other. Second, you need a fluid that will not readily evaporate over the trapping period. The trapping interval in this case was one week. The solution, in a literal sense, was propylene glycol.

Propylene glycol is the major ingredient in antifreeze. One of the problems with it is that it is a sweet substance that is attractive to vertebrates like raccoons and other wildlife. While antifreeze was once dyed green, it is now often dyed pink so as to help discourage its consumption. Another problem with this compound is that it has a really corrosive effect on some invertebrates. Beetles trapped in the pitfalls often begin to disarticulate. Snails and slugs quite literally melt. You can only imagine the putrification factor. Actually, you can’t imagine that.

My supervisor is a graduate student who is simply amazing. She has a great deal of responsibility, but never asks anyone to do something she wouldn’t do. So, she cleaned the samples from one watershed, and I cleaned the samples from the other. Neither of us ever ended up passed out, or throwing up all over everything. Quite a feat, especially considering that ventilation in the lab leaves something to be desired, and the odd salamander or frog that was accidentally trapped only amplified the odor. The worst was a long-tailed (or “masked”) shrew, Sorex cinereus, that just about brought me to tears and seriously threatened to initiate my gag reflex.

Still, the slug slime was probably the most aggravating, not as much for the smell, but for the fact that it blocked the screen of the sieves we were using to filter the specimens from the antifreeze solution. Pouring out a sample with slugs meant you had debris everywhere, not concentrated in the center of the sieve where you wanted it.

The protocol was to check to make sure the label inside the container (urine specimen containers, how appropriate) matched the label on the outside. Then you wash the label over the sieve and set it aside. You pour the contents of the container into the sieve, and then rinse it gently with water from a squeeze bottle. Next, you invert the sieve, give it a sharp tap to dislodge as many specimens as possible into a bowl, and rinse the rest off with 70% ethanol (ethyl alcohol). Lastly, you pour the contents of the bowl back into the container (after rinsing the container). Did I mention that small quantities of detergent are also used to break the surface tension of the liquid agent in pitfalls? Some samples contained enough suds to do a load of laundry.

Ah, but that is all behind us now, and I can hardly wait to get a better look at the actual specimens. The pitfall traps were done a week later than last year’s traps, and the difference was quite dramatic. All the spiders in this year’s samples were much, much larger than those in last year’s! More beetles, too, it would seem. Now, if I can just get all my food to stop smelling like rancid snails….

Thursday, September 10, 2009

Triangle Spiders

An outing to the Westfield River in Hampshire County, Massachusetts last Sunday, September 6, included a stop at the Knightville Dam, where a unique arachnid awaited my discovery. There, among the goldenrods, asters, and ornamental black locust trees I found two triangle spiders, named for the shape of their web: a triangle that is essentially the sector of an orb web. The reduced size of the snare is just one puzzling feature of these amazing spiders.

Triangle spiders belong to the genus Hyptiotes in the obscure family Uloboridae. They are part of a larger group of arachnids called “cribellate spiders.” Cribellate spiders all share one feature in common: an extra spinning organ called a cribellum, located adjacent to the normal group of spinnerets. The cribellum issues a special type of silk that the spider literally “fluffs up” using a comb-like organ called a calamistrum, located on each hind leg.

Perhaps even more amazing than the “accessories” that uloborids have is what they lack. These are the only spiders in North America that do not have venom glands. That’s right, they are non-venomous spiders. So, you ask, how then do they subdue their prey? Great question for which I have not the foggiest answer. They probably do an extra-good job of wrapping their prey in silk, but not just any silk.

The cribellate silk threads in the part of the web designed to trap insects is not sticky like you would expect. Instead, it is tangled, and this is apparently just as effective as little droplets of glue.

Once it has erected its snare, the triangle spider sits on the thread near the tip of the twig or grass stem to which the apex of the triangle is secured. Depending on which book or article you believe, the spider either bridges a gap in this anchor thread, or simply perches there and reels in the slack line to render it taut. When a prey insect impacts the web, the spider then instantly releases the anchor thread, causing the web to rebound, further entangling the prey.

This feat of engineering and strength is performed by a very small animal. Even an adult female Hyptiotes is only 3-4 millimeters long. Males are 2-3 millimeters at maturity. Simply spotting one of these spiders is cause for self-congratulations for any naturalist.

There are four species of Hyptiotes (pronounced Hip-tee-OH-teez) in North America, three of which are chiefly western in their geographic distribution. The one shown in the image here is Hyptiotes cavatus, the sole eastern species.

Keep a sharp eye out for triangle spiders. The webs are mostly build about waist-high in weeds, on bridges and other structures, and twigs of trees and shrubs.