The Wild Party: A Diary of Urban Entomology

Saturday 7 November 2009

Harmonia axyridis (Coleoptera: Coccinellidae), the multicolored Asian lady-beetle, is probably the most common and widespread coccinellid species in temperate regions of the northern hemisphere. It is certainly the most common and widespread coccinellid in my home, where beetles of this species have been coming in from the thickening autumnal cold over the past few weeks. Without much effort, I gathered 10 specimens this morning from just three rooms.

It isn't easy to get 10 lady-beetles to sit still while you photograph them. To settle them down into a quiescent state, I employed the time-honored entomological technique of gathering them in a glass collecting jar and sticking it in the refrigerator for 30 minutes before photographing them. At a dark 44°F (about 7°C), the conditions in the fridge approximate a typical night in October around here, so it calmed them into a sluggish nocturnal state without harming them.

The variations in just my small sample show the pronounced polymorphism of Harmonia axyridis. Individuals can differ dramatically in appearance. (To witness the true extremes of the polymorphic range, see a British survey of specimens found in the London area.) Indigenous to East Asia, H. axyridis was introduced during the 20th century in both North America and Europe as a biological control agent for its unusually vigorous predation of aphids, scale insects, and other agricultural pests. Just one individual can eat up to 12,000 aphids in its lifetime. On another page of this website, I portray all four stages in the life cycle of the species.

Commonly called the harlequin ladybird in Britain, H. axyridis made lurid headlines there when it was first detected in 2004 (in a pub garden) after coming over from continental Europe, where it has been well established for a long time as a biocontrol. The concern in the UK is that it threatens native coccinellid species not only by outcompeting them for food resources but also by actually preying on their eggs and larvae. It is also known to eat the eggs and larvae of moths and butterflies, which are already having a hard enough time in the severely disturbed habitats of modern Britain. H. axyridis is starting to be regarded as a pest over here in North America too, not least by squeamish homeowners who dislike the annual invasion of their indoor spaces.

Nevertheless, I love H. axyridis and must admire its prodigious invasive capabilities. It is one of the lucky species that will assuredly thrive even as the human animal (the greatest invasive species of all) continues to overrun the Earth.

Monday 26 October 2009

At my local train stop, I found one of my favorite insects: the European earwig (Forficula auricularia, Dermaptera: Forficulidae), a species introduced in North America a century ago. I photographed it on a patch of yellow-painted pavement, where it shows up more clearly than it would against dark soil.

The common name earwig is an ancient word that comes to us pretty much intact from Old English éarwicga, first attested in Anglo-Saxon writings around the year 1000. The name reflects the somewhat weird medieval belief that the insects like to enter human ears (they don't). Closely related to cockroaches, earwigs are nocturnal omnivores of soil and leaf-litter. They feed on small arthropods and living or dead vegetation; F. auricularia in particular is known to eat flowers. The wings of earwigs are poorly developed (some are wingless), and in fact F. auricularia cannot maintain flight for long. Indeed, it seldom flies and, like cockroaches, tends to flee danger on fast legs.

However, if cornered, earwigs have defenses. An earwig can swivel its abdomen in almost any direction to fend off predators with its forceps-like rear appendages. For attackers that remain unimpressed by these mechanical weapons, F. auricularia also has a chemical defense: it can spray benzoquinone (C₆H₄O₂), a common malodorous irritant in the arthropodal world, from two glands near the base of the abdomen. It can even coordinate a simultaneous one-two punch of forceps and spray.

From the short and relatively straight forceps (those of males are longer and more curved), I can tell that my specimen is a female. She will soon lay up to 90 eggs in the soil at a shallow depth. There she will guard her eggs from predators, clean them to remove fungal spores, and then overwinter alongside them. Though they are smaller and paler, the young that hatch in the spring essentially resemble adults (i.e. metamorphosis is incomplete). The female will care for her offspring by feeding and protecting them until they disperse. One should not make too much of this famous "maternal" care by female earwigs, for the mother may eat maturing offspring that do not leave her soon enough.

Friday 23 October 2009

Lady-beetles (Coleoptera: Coccinellidae) are migrating into our home in search of warmth. Our resident cobweb spiders are waiting for them.

Several cobweb spiders (Araneida: Theridiidae) have set up webs in the periphery of our living room; some of these are clearly spiderlings, so evidently we have a breeding population.

After a theridiid has trapped its prey and subdued it with its neurotoxic venom, it attaches itself to the body with a firm bite. Then it injects digestive enzymes that liquefy tissues. Eventually, it feeds by sucking up the fluid content of the prey: both its haemolymph (circulatory fluid) and the liquid resulting from the breakdown of tissue by the enzymes. Spiders tend to have long feeding times, and often will feed from different places on the body during the process. My theridiid in the photo above captured its prey on Wednesday night (I know because the beetle was still wriggling in the web). As I type these words on Friday morning, the spider is still feeding.

In the wild, theridiid spiders build their small, bushy webs in any dark nooks or holes they can find: cavities in trees are ideal. However, caves are good habitats for them as well, and to cobweb spiders a building is essentially a cave but even better because it is likely to be warmer and have a greater variety of insect prey: flies, moths, cockroaches, beetles, silverfish, and any other insects that are drawn to humans. Moreover, because they are small and tend to lurk in dark places where people don't care to look, cobweb spiders travel easily with us throughout the world. These serendipitous circumstances explain why theridiids are, unlike many animals, hugely successful in the presence of humans and the structures they erect wherever they go. Indeed, cobweb spiders occur in nearly every building in the world. There is almost certainly at least one in the corners of the room where you are reading this now, and it is probably closer to you than you think.

Wednesday 21 October 2009

After a taste of winter last week, the weather has warmed just enough to rouse insects and spiders from their cold-induced torpor. In the garden at my office, hungry jumping spiders (Araneida: Salticidae) are hunting and feeding again.

While cool autumn air can make flies more sluggish than usual, catching a fly like this is seldom easy, as anybody who has tried to swat them knows. Indeed, salticid spiders are superb little hunters that seek prey freely on the ground or on vegetation instead of trapping it in webs. They locate their prey almost exclusively with the superb stereoscopic vision afforded by their big forward-facing eyes. After spotting and stalking their quarry, they catch it with a lightning-swift pounce of up to several times the length of their bodies. Often a jumping spider will anchor itself to the substrate with a line of silk to prevent it from falling after a leap.

For a fascinating article on the hunting tactics of salticids, see Hunting prey with different escape potentials—alternative predatory tactics in a dune-dwelling salticid, Maciej Bartos, Journal of Arachnology, 35(3), 2007, pages 499–508.

Sunday 18 October 2009

The weather has turned prematurely cold and snowy, so I am cheering myself up with a memory of my time in Bermuda last month. This was a nice place:

I have been unable to identify this spittlebug (Hemiptera: Auchenorrhyncha: Cercopidae), which I photographed near one of Bermuda's small nature reserves.

It may be Clastoptera undulata, a fairly common species of spittlebug that was introduced to Bermuda accidentally, like so many other species, during the 1950s. However, since I cannot track down a photograph of C. undulata, this is just speculation. Nevertheless, remembering Bermuda this evening as the snow coats the roofs and lawns outside has been very enjoyable for me. To read something more intelligent about the family Cercopidae, or just something more intelligent period, do click here.

Friday 16 October 2009

Because it's my birthday today, I am treating myself to a butterfly:

This is a species in the genus Phyciodes, commonly called the crescents. It is probably P. cocyta, the northern crescent; my specimen seems to be a female. Although P. tharos (the pearl crescent) is similar and the two species are easily confused, the presence of this butterfly now, in mid-October, suggests that it is a northern crescent. After its main first generation cycles through life in the early summer, P. cocyta often has a smaller second generation that reaches maturity in September. It is not unreasonable, therefore, to expect some of those adults to be still flying on warm days in the middle of October. The adults of P. tharos, by contrast, seem to fly only during the summer in the northern portion of their range.

Naturally thriving in meadows, P. cocyta seems to do well in the gardens and fields of suburbia. The caterpillars feed on the leaves of aster plants, and the butterflies drink nectar from a variety of flowers, including those of clovers. The caterpillars overwinter to pupate and become the next generation of adults in the following spring.

Tuesday 13 October 2009

Although the annual colonies of eastern yellowjacket wasps (Vespula maculifrons, Hymenoptera: Vespidae: Vespinae) are now close to death as the warm season ends, the workers are still quixotically hunting for protein to feed the doomed final generation of larvae back in the nest. A dead grasshopper will do very nicely. These wasps were scavenging from its body like lions devouring a wildebeest.

The scene of this action was a sun-heated boardwalk through a marsh, now relatively dry, in a forest near my home.

Living grasshoppers (Orthoptera: Caelifera) were plentiful here too, sunning themselves on the exposed woodwork. However, as cold autumnal weather kills their food plants, grasshoppers are in dire need of nutrition. In the absence of living plant matter to eat, normally herbivorous grasshoppers will sometimes feed on dead arthropods—even their own kind.

This grasshopper was feeding on the mangled body of another grasshopper.

Concentrating the nutrients of all the vegetation the dead grasshopper ate while alive, the body provides an efficient source of food in hard times.

Monday 12 October 2009

Found as it warmed itself on the sunny side of a shed, this is my first assassin bug: Pselliopus cinctus.

Assassin bugs (Hemiptera: Heteroptera: Reduviidae) are best known for the tropical species that carry Chagas's disease in South America, but there are many (harmless) reduviid species in temperate latitudes too. All hemipterans have piercing, tube-like mouthparts, but while most use them to feed on plant juices, assassin bugs use theirs to stab insect prey and suck it dry. An assassin bug will also use its mouthparts defensively when it feels mortally threatened, e.g. if a vertebrate predator takes it up into its mouth or if a person handles it carelessly. Apparently, these "bites" are surprisingly painful. Arguably, therefore, the brightly contrasting coloration on many assassin bugs can be considered aposematic.

Pselliopus cinctus has one generation a year, and the adults overwinter after maturing in the summer. Hopefully, my specimen will find a good overwintering place soon, as the weather here is turning cold with dismaying speed.

Saturday 10 October 2009

The weather here has chilled as autumn deepens. Insects and other arthropods are increasingly hard to come by as they either die or seek hidden sheltered places in which to overwinter. However, when you do find them now they are relatively easy to photograph, being sluggish and slow in the cold. (This is one reason why birds forage so early in the morning: even during summer, the air is often cool enough to slow down their prey conveniently.) Today I found a lady-beetle, a typical specimen of the introduced species Harmonia axyridis (Coleoptera: Coccinellidae), which I have written extensively about elsewhere.

In warm temperatures, coccinellids are vigorously active and seldom keep still long enough to photograph well, especially after you have intruded on their space and they know you are there. Today, however, my specimen of H. axyridis was too chilled to flee.

In fact, it repeatedly sought the warmth of my hand while I was manipulating its leaf for the photograph. It will soon need to find a proper shelter for the winter. Like many coccinellids in temperate climes, H. axyridis sometimes congregates in large numbers inside warm places, including houses, during the cold season. While I think having a festive swarm of coccinellids in my home would greatly enliven the dark depths of winter, this always seems to happen to homeowners who fail to appreciate the phenomenon.

Monday 5 October 2009

Having flourished all summer, colonies of yellowjacket wasps are now reproducing on warm days in the early autumn. Young queens and males are flying out of their mother colonies, never to return, on a one-way trip to mate with counterparts from other colonies. I found this young queen yesterday near my home:

The species seems to be Vespula maculifrons (Hymenoptera: Vespidae: Vespinae), the so-called eastern yellowjacket, a common species in my region. After mating with a male from a different colony than her own, she will seek a sheltered nook in which to overwinter until the spring, when she will found her own colony. All of the sperm she needs to produce hundreds of offspring will be contained in her abdomen. And so her life's journey has only just begun.

It is a different story for the males. Not far from my young queen, I spotted what I think is a male of the same species:

If he was lucky, he has mated with a young queen like the one in the prior photograph. Hopefully this is so, for he, unlike the young queen, certainly has no future left now. When I found him, he was too exhausted to fly and could only creep along in the grass. Indeed, male yellowjackets exist solely to mate. Once they have inseminated a female, their purpose is spent. The colony that nurtured them to adulthood during the summer is no longer their home. They will survive for as long as they can on their own, but as autumn deepens they will, ineluctably, die alone out in the world from starvation, cold, or predation.

Meanwhile, the colonies of workers, led by a queen, that thrived all summer are starting to die too. By the first frosts, all the workers and old queens will be dead. The next annual generation of yellowjacket wasps will then depend entirely on the young queens that overwinter in leaf-litter, under logs, and in the soil.