Archive | July, 2010

Camping Caterpillars

30 Jul
Tent caterpillars in webbing.

Tent caterpillars in webbing (Sam Houston National Forest).

These gregarious caterpillars get their name from the elaborate ‘tents’ of webbing around they weave as a unit.  There the young caterpillars dwell in relative safety, warming themselves early in the year, and escaping the high temperatures that may occur later in the year.  The layers of webbing forming the ‘tent’ create a range of temperatures which allows the caterpillars to thermoregulate efficiently.  Here you can see where the webbing has been torn open to reveal the mass of fuzzy orange caterpillars beneath.  The caterpillars leave the tent to forage, laying down scent trails to find their way back and to alert tentmates to tasty finds.  This behavior is remarkably similar to that of ants.

Tent caterpillars are members of the moth family Lasiocampidae.  Adults are typically dull brown and somewhat fluffy.

Tent caterpillars.

An opened nest of tent caterpillars.

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Skippers

26 Jul
Skipper (Hesperiidae) at rest.

A skipper pauses briefly on a plant stem.

Most people are comfortable differentiating butterflies and moths.  However, as with most biological groupings, especially those based more on appearance and habits than taxonomy, exceptions and ambiguities run rampant.  One particular example, is that of the ‘skipper.’  Perhaps this common name is, in fact, commonly used by other laypeople, but I had never heard of it when I entered entomology.  If I had seen a skipper in the field, I would probably have assumed it was a moth still out in the daylight, or a somewhat odd and drab little butterfly.

In fact, skippers are a subgroup of butterflies, comprising the family Hesperiidae.  They resemble a cross between a moth and a butterfly, but can be easily recognized by several features.  They have large, wideset eyes on a broad head, one of the characteristics that lends them a moth-like appearance.  Their antennae are also widely set, not meeting at the base, and have hooked clubs at the ends.  Their stocky bodies tend to be fairly fuzzy or fluffy looking and they have drab to moderately bright coloration.

Skippers are active in the day time, and take their common name from their quick, short flying style.  Many species look quite similar to each other and can be difficult to distinguish.  These butterflies are both extremely common and widespread.  I took the photo above of a skipper in Argentina, while the mating pair below I spotted in the Welder Wildlife Refuge in Texas.

Two mating skippers perch on a leaf.

Two mating skippers perch momentarily on a leaf.

At the Aphid Bar

23 Jul
Sugar ant (Brachymyrmex) tending aphids on flower bud.

Sugar ant (Brachymyrmex) tending aphids on flower bud.

As mentioned in a previous post, many phloem-feeding hemipterans, such as aphids, take in excess sugar, which they excrete as a substance called honeydew.  This sugary substance attracts other sugar feeding insects, which has led to some interesting interactions.  Among the most notable is the development of a mutualistic, or symbiotic, relationship between some ants and aphids.  Ants may ‘tend’ aphids, drinking the honeydew and protecting the aphids from predators in return.  This provides the additional benefit to the aphid of preventing the build up of their sugary excrement which could encourage the growth of fungi and mold.

Carpenter ants (camponotus) tending aphids.

Carpenter ants (Camponotus) tending aphids. A parasitic wasp perches on the edge of the leaf.

Ant-hemipteran interactions can be observed almost anywhere if one takes the time to observe closely.  I found the carpenter ants above tending aphids on the bushes right outside my front door.

Of course, as in any biological relationship, cheaters exist.  Some ants tend aphids without providing any protection against predators.  Some aphids manufacture less nutritious honeydew.  On the other hand, some ants take their care of aphids to extremes, even building structures to protect the aphids against winter cold.

Silhouette of carpenter ant tending aphids.

Silhouette of carpenter ant tending aphids.

Sunny Suckers

19 Jul
Aphids on a flower.

Aphids nestle under the base of a flower in Sam Houston National Forest.

Anyone who has spent much time around plants will be familiar with this classic gardener’s pest, the aphid.  Aphids use their piercing-sucking mouthparts (a characteristic of the order Hemiptera)  to drink the fluids of plants.  Fluid uptake occurs passively via the pressure generated by the plant’s own circulatory system.  In fact, the aphid’s mouthparts actually contain valves to limit the flow.  Without such systems the aphid would literally be blown off the plant.  It is more the equivalent of attempting to drink from a firehose than sucking from a straw.

Aphids are gregarious insects which live in small subsocial colonies on plants.  Reproduction varies among aphid species and may be sexual or asexual.  Many aphid species give live birth to young.  In the picture above and below, a few white and shriveled cast off exoskeletons are visible from developing aphids.  These skins, called exuvia, can become quite numerous as colonies grow and become crowded.  Overcrowding on plants generally triggers the production of winged aphids, which disperse to new host plants where they found new colonies.

Aphids coat a plant stem.

Aphids coat a plant stem in Argentina.

Fishflies and more

16 Jul
Male fishfly on tree trunk.

Male fishfly on tree trunk.

I took these pictures at a lightsheet in Sam Houston National Forest.  Fishflies, alderflies and dobsonflies are some of the strangest looking nocturnal critters you may run across.  Large, soft-bodied, and wriggly, the aquatic larvae of some of these species are popular as bait with some fishers*.  Male dobsonflies have hugely elongate mandibles, sometimes an inch long;  however, these jaws are adapted for mating purposes and cannot inflict harm on humans.  Other members of this family, including female dobsonflies and the aquatic larvae, can inflict a painful bite with their shorter jaws.  While the larvae are active predators and scavengers which may live several years in the water, most of these insects live only briefly in their winged, adult form, and do not feed.

Male fishflies lack the imposing jaws of male dobsonflies, but can be distinguished from females by the extra fringe on their antennae (compare the picture of the male, above, with that of the female, below).  In many insects, the responsibility for locating a mate falls to the males, who may have highly developed sensory organs for this purpose.  These may include enlarged eyes, antennae, or ‘ears’ to detect signals from females.  These male fishflies will use their antennae to pick up pheromones released by females.

Female fishfly on lightsheet.

Female fishfly on lightsheet.

These insects are members of the order Megaloptera (sometimes grouped as a suborder with Neuroptera) and the family Corydalidae.

Fishfly on finger.

Fishfly on finger.

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*UNRELATED EDIT:  My sources inform me that the correct term is ‘fishermen’ rather than ‘fishers.’  But what of the poor, overlooked fisherwomen?  I suppose the term ‘fisherpeople’ does sound a bit off.  From now on I’m calling them ‘fishpeople’ and have done with it.

In a Name – lady beetles and insect naming

12 Jul
Ladybug

Ladybug in the leaves.

Here’s the familiar adult form of the strange little guys from the last post.  These are commonly known as lady beetles, ladybugs, and sometimes even ladybirds.  Ever wondered about the difference between ‘ladybug’ and ‘lady beetle’? (Too bad, I’m telling you anyway!)

Here’s an interesting little trick I learned for figuring out the correct spelling for those weird mix-up common names that pop up frequently in insects (and other groups!).

If the insect name contains a word that describes a group it is actually part of, that word can stand alone.  So, in the case of the beetle above, we get ‘lady beetle.’  Another good example of this would be ‘horse fly,’ which is, in fact, a type of fly. (But not a type of horse.)

If the insect name contains a word that describes a group it not actually part of, the words are run together.  So, we have ‘ladybug’ and ‘ladybird.’  Most people will have no problem remembering that a ladybird is not actually any type of bird.  The ‘bug’ question may seem a bit more confusing, but remember ‘true bugs’ belong to the familyHemiptera.  Beetles are not ‘true bugs.’  Thus, ‘ladybug,’ all one word.  Other good examples of this are ‘butterfly‘ and ‘dragonfly,‘ neither of which are flies.

What’s the point of this?  Well, you can hazard a good guess that armyworms and silkworms aren’t actually worms. In fact, they are both types of caterpillar (butterfly larvae).  Similarly glowworms is a widely used common name for a number of insect larvae, including those of fireflies.  For that matter fireflies aren’t flies–they’re beetles!

Don’t get carried away, however.  While yellow jackets are not actually jackets, it is perfectly acceptable to leave the space. (A yellow jacket jacket would be uncomfortable.)

Minute Monster – the immature ladybug

9 Jul
Baby ladybugs!

Baby lady beetles munching aphids.

Another picture from right in my backyard!  Unlike their pretty and popular adult form, ladybug larvae look a bit like they ought to be featuring as monsters in a horror movie, and they are indeed fearsome predators.  (At least of the very tiny.)  But just like grown up ladybugs these strange critters are the gardener’s friend, since their favorite prey are aphids.  Another trait they have in common with adult lady beetles is their bright coloration.  This aposematic, or warning, coloration serves to alert predators that they are not good to eat, due to the toxic chemicals they sequester in their bodies.

Lady beetles belong to the family Coccinellidae, which takes it name from the word coccus, meaning circular, due to the adult beetle’s nearly circular shape.  They are also generally almost flat on the bottom, allowing them to draw their legs under their armored exoskeleton and fit almost perfectly against a plant surface when under attack.

Le Pew – the Stink Bug

5 Jul
Stink bug on tree

A stink bug climbs a tree.

These large, cryptic stink bugs have been hanging around the trees by my house lately, often clustered up against the bark and nearly undetectable by casual observation.  Like other hemipterans, stink bugs (or pentatomids) have sucking mouthparts, which they use to feed on plant matter.  We also have a fairly common bright green stink bug that does a good job blending in with leaves and stems.

Stink bugs get their common name from the strong deterrent odor they emit when disturbed.  This smell, combined with an unpleasant taste, helps to ward of predators.  This is not unique to stink bugs, however:  several other hemipteran families also have scent glands.  Unlike such smelly animals as the skunk, I find the smell of stink bugs not particularly unpleasant–a bit like sickly sweet fruit.  A casual survey of various people I have had the opportunity to quiz on the subject (“Here: smell this bug!”)  supports my opinion.

The stink bug family name Pentatomidae means “five divisions”  which may refer to the five-segmented antennae (many other hemipterans have only four) or the somewhat pentagonal body shape.

Stink bugs clustered on bark

Cryptic stink bugs on bark.

Katydids and Didn’ts

2 Jul
Katydid nymph on a leaf.

Katydid nymph on a leaf.

Katydids are a member of the order Orthoptera (grasshoppers, katydids, crickets, etc.) and the family Tettigoniidae. Orthopteran nymphs, or immatures can be distinguished from adults by the development of their wings.  Only adult insects have completely developed wings (think butterflies, beetles, and flies).  Immature insects have not yet developed wings (think caterpillars, grubs, and maggots).  Katydids, like other orthopterans, have incomplete metamorphosis, meaning they lack a pupal stage (think chrysalis or cocoons).  Instead, the immatures generally resemble the adults in appearance, and partially developed stubby wings, called wing pads, may be present in some of the later molts.  The nymph above is very young, and has no wings or wing pads present.

Here’s a picture from my own backyard in Texas!

A katydid nymph on a leaf.

A tiny katydid perches on a leaf.

Katydids are also called ‘long-horned grasshoppers’ in reference to their long antennae.  Orthopterans of the suborder Ensifera, or ‘sword-bearing’, generally have antennae longer than their body length as well as exserted ovipositors (sword-like egg-laying tubes that allow females to saw their eggs into plants or insert them down into the fround.)  Thus, katydids (like crickets) can be distinguished from grasshoppers by their long slender antennae and legs.

Below, you can see a grasshopper nymph, from the suborder Caelifera.  This grasshopper is a member of the family Acrididae, the ‘short-horned grasshoppers.’

A grasshopper nymph perched on a fingertip.

A grasshopper nymph perched on a fingertip.