Archive | June, 2010

Cradle Robber

28 Jun
A carpenter ant worker carries off a Pseudmyrmex pupa.

A carpenter ant worker (Camponotus) raids a Pseudmyrmex pupa from an opened nest.

While watching  Pseudomyrmex workers in an opened nest carry brood to safety (see previous post) I noticed one ant that didn’t belong.  Above you can see a carpenter ant worker who has taken advantage of the confusion to steal one of the helpless juveniles.  Although some species of ants practice brood-raiding in order to aquire ‘slave’ ants, this unfortunate Pseudmyrmex pupa will merely make a tasty meal.

Baby Ants

25 Jun
A nest of Pseudomyrmex ants.

An opened twig reveals a nest of Pseudomyrmex ants

I accidentally opened up this nest of Pseudmymex ants in Argentina while trying to see where a worker carrying a caterpillar had got to.  This promoted a flurry of activity as workers grabbed brood to carry to safety.  The pale white ants are, in fact, immobile pupae (the equivalent of a cocoon or chrysalis in a butterfly) getting ready for their final molting into active adults.  You can see one dark pupa that is nearly ready to eclose.  The small white objects are eggs, but no larvae appear to be present in this portion of the ant nest.  Ant larvae look a bit like small grubs or maggots.

Pseudomyrmex are occasionally called twig ants.  The genus name, Pseudomyrmex, means “false ant,”  because the original descriptor of this genus thought he had discovered an ant-like wasp.  Pseudomyrmex are very interesting ants.  Fairly large, if slender-bodied, manyPseudmyrmex species live in relatively small colonies (often only 30 to 80 individuals, compared to the hundreds of thousands seen in species like fire ants). Individual workers forage alone, able to take down prey and return it to the nest without assistance.  Personally, I call these ants tiger ants–fierce, sleek, and deadly solo hunters.

These ants also include the acacia ants, and other tree symbionts, whose colony sizes can number in the millions.  In these mutualistic systems the tree provides the ants with specialized food and nesting space and the ants fiercely defend the trees.


21 Jun
Wolf spider and egg sac

A mother wolf spider and her egg sac.

Ran across this huge wolf spider in Argentina.  She was sitting smack in the center of an equally huge cow patty, which is not exactly photogenic, but at least she showed up nicely.  Under her abdomen you can see her egg sac, which looks nearly bigger than she is.  This is one way in which female wolf spiders provide parental care; by wrapping their eggs up in a silken ball, and carrying it with them to protect it from predators. Many also carry the newly hatched spiderlings on their abdomen.

(Of course, as always, there are ways around this.  For instance, one very strange little group of insects, the mantispids, are important predators of spider eggs.  In cases where the silken case is too difficult to chew through, some species’ larvae will actually follow a spider around and get themselves spun into the egg case.  But I’ve gone off on a tangent.)

Wolf spiders hunt sans web, prowling the ground and tackling prey one-on-one. They take their name from their hairy appearance and hunting style.

Pretty Plumes

18 Jun
Larvae on leaf.

Gregarious insect larvae eating a leaf in Argentina.

These little guys were tiny enough to overlook easily, but bizarre and striking on close inspection.  I am informed that the peacock like ‘plumes’ on the ends of these insects are likely to be made from cast skins or even ‘tubes’ of excrement.  The beauty of nature.

A leaf-skeletonizing chrysomelid larva on an arm.

A chrysomelid larva on an arm.

Insect larvae can be tricky to identify, but general consensus among entomologists I showed this to, is that these are some sort of chrysomelid (leaf beetle) larvae.  The family Chrysomelidae is a large and diverse group of small to medium sized beetles which take on a variety of forms, but tend to be found feeding on plants in both the larval and adult forms.  These particular larvae appear likely to be skeletonizing leaf beetles*, so named from the manner in which they feed off the plant, and the leaf ‘skeleton’ left behind.  Like many insect larvae, these appear to be somewhat gregarious, as I observed them mostly in small groups.

Two tortoise beetle larvae (Cassidinae) with dimorphic coloration.

Two chrysomelid larvae with dimorphic coloration.

*Update:  Laura suggests that these should be Cassidinae, or the larvae of tortoise beetles (see comments).  Tortoise beetles are fabulous little critters, so I’m thrilled to learn that their babies frequently make dramatic poop structures.

Inside a Gall

14 Jun
A gall formed by a juvenile insect.

A juvenile insect inside an opened gall.

Galls are highly variable plant structures which can be formed by a number of causes.  They usually appear as an abnormal swelling in a leaf or stem.  Insect galls are caused when an insect uses chemicals to seize control of a section of plant tissue, stimulating it to form a favorable habitat for a juvenile insect.  The gall provides both shelter from predators, as well as food and moisture.

A number of insects have independently developed gall-forming abilities.  These include gall wasps, gall flies, gall midges (a small fly), aphids, and more.  In many cases the adult insect injects an egg into the plant, where it then develops into a larvae and pupae, and finally emerges as an adult.  Galls are not entirely safe from predation–many insects have developed strategies for getting at the developing young.  For example, a number of parasitoid wasps inject their own eggs into the developing gall inhabitant, which is consumed as food by the new parasitoid.


11 Jun
Parasitoid wasps at an eggcase.

Parasitoid wasps parasitize an insect egg case.

Found these tiny wasps parasitizing a mantis egg case or ootheca in Argentina.  You can see the tiny wasps rearing up and inserting their long ovipositors.  In higher members of the order Hymenoptera, the female ovipositor is modified into the sting (only female bees, wasps, and ants can sting.)

‘Parasitoids’ are distinguished from ‘parasites’ in several ways.  A parasitoid insect lays one or multiple young on or into a single host organism–often a juvenile or egg.  The young develop inside the host, which may live on for some time, but almost always ultimately succumbs to the creature devouring it from the inside out.  Anyone who has watched the movie Aliens may find this sequence of events familiar.  Parasitoids thus are not true parasites as they kill their host, but not quite predators, in that they consume only one prey item during the course of their lifespan.

Flower Power

7 Jun
An orchid mantis on flowers.

An mantis lurks on flowers, awaiting prey.

I found this flower mantid doing as it’s name might suggest in Argentina.  The most well known flower mantis is the Malaysian orchid mantis, a striking pink flower-mimic.  These particular flowers were buzzing with insect activity, so this mantis had found a good hunting spot.

Like many insects which lack a pupal stage (such as a cocoon or chrysalis), immature and mature mantises can be distinguished by the development of the wings. In this juvenile mantis (called a nymph), the two pairs of partially developed wings are visible as ‘wing pads’ just before the down-turned abdomen.  The wings will only be fully formed after the final shedding of the exoskeleton as the mantis achieves its final adult form.  Only adult insects have wings, although some species, such as worker ants, walking sticks, and burrowing roaches have become secondarily wingless in the adult form.

Here’s another shot.

Sister, sister

4 Jun
Dimorphic carpenter ant workers at a nest entrance.

Dimorphic carpenter ant workers at a nest entrance.

The fine hairs on these Argentinian carpenter ants (genus Camponotus)  gave then a pretty golden sheen.  I spent a while watching the workers of this colony.  Clots of dirt extracted by diggers in the nest can be seen scattered around the periphery of the nest entrance, and form a large ring a few centimeters out.  The ants didn’t approve of my looming camera lens and I caused a bit of commotion in the ranks.

Like other eusocial insects such as termites and bees, ants divide tasks up among members of the colony.  In this case the daughter ants of the queen can take several developmental paths.  The vast majority develop into infertile workers, which carry out tasks such as nursing the young, tending the queen, building and maintaining the nest, foraging for food, and defending the colony.  As with many ants, the workers of carpenter ants are polymorphic– they may develop into different body forms, specializing in different tasks.  The large, broad headed and strong jawed ants such as the one seen above standing guard over the nest entrance are called ‘majors’.  The smaller, more typical ants such as the forager seen to the left returning to the nest, are called ‘minors.’

Many people are familiar with the concepts of ‘soldier’ and ‘worker’ ants.  The reality is more complex.  Some types of ants do not have polymorphic castes, or have a continuous range of worker sizes from small to large.  In some species of ants, the larger ants do indeed function as soldiers, while in other species they are more like pack animals, specialized for carrying large amounts of food back to the nest.  In some types of leafcutter ants, the minors ride on leaf cuttings carried by majors and defend the large ants from attacks by parasitic flies.  Smaller minors tend to be the primary nurses, as in many types of ants the major’s large jaws makes brood handling difficult.  However, in probably the majority of ants, workers progress through tasks with age, with dangerous jobs outside the nest generally relegated to the oldest workers.

The concept of the eternally busy and hard-working ant is equally inaccurate.  For example, in the typical fire ant nest, workers will often spend half their lives or more as ‘reserves’ available to be called on for a variety of tasks but otherwise inactive surplus.

Camponotus Nest

Ring of dirt around a Camponotus nest entrance.