Life of a carpenter ant

Carpenter ant pupa cocoon and first instar larvae.

Ants, like butterflies, are holometabolous and go through complete metamorphosis with an egg, a larva (~caterpillar), a pupa (~chrysalis/cocoon), and adult ant (~butterfly).  In ants, the larvae resemble small white grubs and cannot move by themselves–they are fed and tended by the worker ants.

Carpenter ant first instar larvae viewed under magnification.

The larvae are covered in fine hairs which help them stick together in clumps, making it easier for adult workers to move and tend them.  In fire ants, these hairs also help with rafting behavior, because they can trap a layer of oxygen around the larvae, helping them breathe and making them extra buoyant.  Rafting fire ant colonies use their babies as tiny floatation devices.  Please take a moment to consider the wonder of nature.

As they grow, the larvae molt several times, and each growth stage is referred to as an instar.  The larvae pictured above are extremely tiny because they are first instar larvae, having only recently hatched.

A pupating carpenter ant larva after spinning her cocoon.

When the larvae are old enough they prepare to metamorphose into adults.  Some ants, like these carpenter ants, spin themselves into cocoons to pupate, while others, like fire ants, leave their pupae exposed.  Above, you can see an opened cocoon that contains a larvae that has not yet molted into its pupal form.

Additional fun fact: ant larvae have a closed digestive tract (I assume to prevent them from making a mess all over the colony.  It’s like the ant equivalent of diapers.). They poop for the first time when they molt into pupae.  Best line from a paper ever:  “…the larva defecates for the first time…. Workers help out.” (Taber, 2000).  This is also the least appealing job description.

A carpenter ant pupa in her opened cocoon.

While the job of the larva is eating and growing, the job of the pupa is developing–reorganizing its system into an adult ant.  Ant pupa look basically like unmoving, pale adult ants, darkening up right before their final molt to adulthood.  The newly molted ants are still fairly pale and soft-bodied.  They are referred to as “callows.”  Their exoskeleton darkens as it hardens, until they are prepared to go about the daily business of an adult worker ant.

Adult carpenter ant worker.

PS:  Here is a cool video of a queen ant helping a pupa shed its old larval skin.

Green Rooms and Gall Wasps

Eucalyptus leaf galls formed by gall wasps.

This is a green bug for St. Patrick’s day.  (I’m reaching; I know.  Happy Birthday, Eric!)

I’ve talked a bit about gall-forming insects in the past, but I think it bears repeating how extremely cool this adaptation is.  Galls are created by parasites (fungi, bacteria, mites, wasps, aphids, flies, midges, psyllids, etc.)  that use chemicals to co-opt the physiology of their host and cause the plant to grow abnormal structures that make a comfy little home for the parasite in question.  Opening up these particular leaf galls revealed tiny wasp pupae, developing in the safety and luxury of their own private green room.  Chemical warfare at it’s most refined.

Tiny gall wasp pupae inside a leaf gall.

P.S.  Does anyone know if any wasps outside Cynipidae form galls?  That’s the only family I’m familiar with.

Christmas Mystery Cocoon

In honor of Christmas and the season of giving I bring you this mystery stocking stuffer, encountered in Argentina.

First, the present all wrapped up and hung on the tree.

Peeking inside...

Removing the first layer of wrapping...

The mystery present all unwrapped.

Ta-dah!  Your present seems to be some kind of hymenopteran pupae.  And if you can tell me what they are, that will be my present.

…merry Christmas and happy holidays, y’all!

Life Cycle – Red-headed Chrysomela leaf beetle

A red-headed Chrysomela leaf beetle (Chrysomela texana).

These  red-headed Chrysomela leaf beetles were all over the park near my home this week, mostly in the vicinity of a large willow tree, the beetles’ food of choice.  Chrysomela texana are close relatives of the cottonwood leaf beetle (Chrysomela scripta).   C. texana can be easily distinguished by it’s red pronotum, head, and underside (most similar species have distinct black markings on these areas).  Every life stage of the beetle was apparent, from the yellow eggs laid in clusters on a leaf, to the lady beetle-like black and brown larvae, skeletonizing the surrounding vegetation in gregarious clusters, the red-brown pupae.

A cluster of yellow red-headed Chrysomela leaf beetle eggs on the underside of a leaf.

(Note: The egg hunt was successful.  Happy Easter!)

A gregarious cluster of red-headed Chrysomela leaf beetle larvae skeletonize a willow leaf.

Like swallowtail caterpillars, the larvae have cool, eversible glands which they use to secrete defensive chemicals (as pictured by Mike Quinn on BugGuide).  The pupae of these beetles were particularly abundant.  They seemed to be stuck to every surface I looked at–tucked under bark, into crevices, dangling from leaves and even from small flowers and weeds.  This gave me the chance to snap the pictures below of a beetle struggling out of its pupal case. I even took a few home, but they were sneaky and eclosed on me when I wasn’t looking.

A red-headed Chrysomela leaf beetle (Chrysomela texana) ecloses from its pupal case.

A red-headed Chrysomela leaf-beetle ecloses from its pupal case.

Cast off pupal case of a red-headed Chrysomela leaf beetle.

*edit*

Surprise bonus image!  Now the life cycle is complete. 😉

A mating pair of red-headed Chrysomela leaf beetles (Chrysomela texana).

Queen Ants – Founding a new colony

A foundress carpenter ant queen (Camponotus) tends her clutch of eggs, with her dropped wings visible in the foreground.

Lots of pictures of queen ants today.  While the huge diversity of ant species have developed numerous methods for founding new colonies, a few strategies are fairly widespread in the ant world.  After a nuptial flight, in which winged sexual male and female ants mate,a future queen faces the harrowing challenge of founding a new colony.  With her ovipositor specialized for egg-laying she cannot even sting or spray venom.  She has only her jaws to defend her and she is heavy-bodied and clumsy.  Mortality is high–one reason ant colonies pump out vast flocks of winged alates.  Dropping to the ground the new queen searches diligently for a nest site, shedding or pulling off her now useless wings so that she can burrow or explore small crevices more easily.  The energy from her atrophying wing muscles will be used to help feed her and her developing brood.

A foundress carpenter ant queen stands guard over her eggs after being disturbed.

Unless she manages to join an existing nest (some ant species such as fire ants will accept additional queens into established colonies) or co-founds with a small group of other queens (in which case surplus queens may later fight or be executed by workers) she will be alone until she manages to raise her clutch of eggs through the helpless larval and pupal stages and into small adult workers.  In some species queen ants take on the risky task of foraging for food, but in many species queens practice claustral founding, closing themselves away into small nest chambers until the first workers eclose, relying entirely on the resources stored in their bodies to provision them.

A cloistered fire ant foundress (Solenopsis invicta) with her brood.

During this time, queens carefully tend their precious brood, feeding them via  salivary secretions or trophallaxis (regurgitation) and grooming them to prevent mold or fungal growth.  Fire ant queens lay trophic (feeding) eggs, which they eat and then regurgitate to the larvae.

A foundress fire ant queen in a test tube tends her first larvae and pupae.

The first workers pupate prematurely, and eclose as unusually tiny adult ants, called minims or nanites.  The pale, callow workers slowly darken and gain mobility as their exoskeletons harden.  Driven by hunger and instinct, these tiny workers open up the colony and venture carefully forth for the first foraging expeditions of the colony. (Other tactics may also come into play–fire ant minims practice brood raiding, where they steal developing larvae and pupae from nearby colonies to enlarge their own labor force.)  Later workers, tended by the minims and better provisioned with food, will develop normally into typically sized workers of the various castes.

A foundress fire ant queen (Solenopsis invicta) tends her brood with the help of newly eclosed minim workers.

As the worker population increases, the queen’s careful attendance of the brood slackens and her primary role in the colony becomes egg-laying and remaining alive. Rather than standing to defend her only clutch of brood queens now have a horde of daughters to defend the nest, and they retreat from any signs of danger or disturbance to the nest.

An acrobat ant queen (Crematogaster) in formacarium with brood pile, nurses, and newly eclosed workers.

These pictures are mostly foundresses I’ve captured hunting nest sites and reared out in test tubes.  Ant colonies are fun to keep, and ridiculously easy to found (what other pet can you close away in a tube and ignore for the first month?).  For the purposes of my research I’ve mostly reared fire ant colonies, and these are the main foundresses I encounter in my area of Texas (good for my research, not so good for the ecosystems they’ve invaded).  Obviously not the ideal pet ant colony, but in a secure environment they are fun to observe and they make for sturdy, fast-growing colonies.

Fire ants!

A fire ant worker in a laboratory foraging experiment climbs the wrong post and misses the sugar bait.

Amazingly I have somehow made it to my 6th month of regular posts without bringing up my favorite little study organism–the fire ant!

Let’s remedy that immediately.

My current research project involves studying variation in foraging behavior of the red imported fire ant, Solenopsis invicta.  Since I could talk about fire ants for a loooong time, this is going to be a bit of an odds and ends post where I just throw some pictures at you that I find interesting.  If you live in the south eastern United States (or California) you’re familiar with a sight something like this:

A colony of fire ants swarms in response to a disturbance to the mound.

Disturb a mound of fire ants and you are very quickly greeted by hundreds and even thousands of angry workers swarming up in defense of the colony.  In the above picture the worker ants are swarming a straw which has disturbed their nest.  (Note: never attempt to drink a fire ant colony.)  Fire ants react both to vibrations (such as footsteps) and changes in air flow (such as might be caused by breath, or a disturbance to the mound).  The workers release alarm pheromones which alert and recruit other workers to the site.  Fire ants are (in)famous for their painful stings, which have been described as a fiery, burning sensation.  In particular, their tendency to swarm and sting en masse makes an encounter with these ants potentially very unpleasant.

Fire ant sexuals and polymorphic workers.

Like other ants, the majority of a colony is made up of wingless, sterile female workers.  Sexual, or reproductive ants, called alates, are the only members of the colony who develop wings.  These wings allow them to disperse in mating swarms (called nuptial flights).  Male fire ant alates can be distinguished from females by their darker coloration and smaller heads.  (As it was once put to me, they have ‘big shoulders and tiny brains–typical males.’)

After the mating flight, fire ants drop to the ground.  Males die shortly thereafter, but the females must now attempt to join a new colony or establish their own.  These queens (or sometimes ‘gynes’) dig a small chamber and close themselves in.  The queens shed their wings, and and use the energy from their wing muscles to feed their eggs and developing brood until the first tiny workers (called minims, or nanites) mature and leave the nest to forage.

Brood development of fire ant queens and polymorphic workers. Left to right: two points in development of larvae, two points in development of pupae, and the adult form.

Fire ants, like other Hymenoptera, have complete metamorphosis (holometabolous) and undergo a resting, pupal stage as they transition from larvae to adults.

Fire ant workers are polymorphic–adult workers may mature to a broad range of sizes.  Although these sizes range across a continuum and there are no discrete castes (as exist in some other ants) workers are often grouped into broad size-based categories: majors and minors.  Ants towards the middle of the size continuum are sometimes called ‘medias.’   Worker size influences both lifespan and performance at different tasks.  For example, majors, with their large jaws, make poor nurses but excellent carvers and heavy lifters when foraging.

Polymorphic worker ants and brood (Solenopsis invicta).

Cradle Robber

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

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.

Inside a Gall

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.