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.

In Defense of Caterpillars

A swallowtail caterpillar everting its osmeterium.

Here’s an immature form of the swallowtails we saw in the last post.  Late instar swallowtail caterpillars like the one above have aposematic coloring, warning of the toxic chemicals they have gradually sequestered from the plants they eat.  Swallowtail caterpillars also have another unique defense mechanism–an organ called the osmeterium, located in the head.  When threatened, caterpillars evert the osmeterium, which resembles two brightly colored fleshy ‘horns’ on the caterpillar’s head.  The osmeterium emits foul-smelling terpenes which, along with the startling appearance and the caterpillar’s thrashing movements, helps to ward off predators.

Casebearers

A case-bearing leaf beetle laravae (Chrysomelidae: Cryptocephalinae)

Anyone noticing one of these small brown objects on a leaf could easily dismiss it as bird droppings.  Only a close look will reveal their secret–these cases house hungry beetle larvae, who can munch on the leaf in the security of their protection and disguise.  For my own part I only discovered these insects when I took a closer look at some of the contents of my sweep net.  They seem to be relatively common in Texas in the late spring as I turned them up frequently at a number of field sites.

These insects are a type of leaf beetle (family Chrysomelidae), belonging to the sub-family Cryptocephalinae (literally “hidden head”), the case-bearing leaf beetles, or casebearers.  (For those not up to date with Latin naming conventions, the “-dae” suffix is used to indicated families, and the “-nae” suffix is used for subfamilies.)  The ‘case’ is a gift provided by the mothers–they wrap the eggs in layers of fecal matter, which the larvae later add to.

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).

Fuzzy Wuzzy Was A (Wooly) Bear

A tiger moth caterpillar climbs a grass stem.

When I was little I was always taught not to touch caterpillars because they might sting.   ‘Especially the fuzzy ones.’   This training has survived in me and even today I am leery of the fuzzy variety of caterpillars, despite knowing that the stinging caterpillars are vastly in the minority and fairly distinctive.  Luckily, friend and caterpillar expert Laura Ann was with me when I encountered this particular fuzzy fellow in the Welder Wildlife Refuge, so I not only had the opportunity to pet the little guy, but to try him out as a mustache and unibrow.  He was a bit too active for either post.  “Arctiids are fast,” Laura Ann pointed out helpfully, as my temporary unibrow made its escape.

A fuzzy black tiger moth caterpillar.

Tiger moths, family Arctiidae, take their name from the pattern common on many members’ wings, which often includes orange and black markings on a white background.  These are relatively common visitors to light sheets here in Texas.  Their caterpillars are often fuzzy, giving them the common name “wooly bears” or “wooly worms.”  Like other caterpillars, its prolegs (the additional pseudo-legs it has as a larvae) are equipped with one or two rows of tiny curved hooks called crochets (see prolegs on the picture above).  The hooks allow them to climb smooth surfaces like plant stems and leaves.  The patterns and placement of these hooks are used for identifying many immature Lepidoptera.

Pit Monsters – The Immature Antlion

An antlion larvae removed from its pit.

An antlion larvae, viewed up close, is a truly creepy little critter.   It is one of those horror movie-esque predators that makes me very glad I am not insect-sized.  If you remember the pit monster from the original Star Wars movies you have some idea what these guys are all about.  Antlion larvae are famous for the conical pit traps they build to catch their prey.  The antlion larvae finds a fine, sandy soil and moves in backwards circles, burrowing down and flicking sand up to create a funnel above it.  (In fact, pit-building antlions have adapted to a point where they can no longer move forwards.)  The antlion larvae lurks at the base of the pit, ready to grab any small critters that fall down the slippery sides of the pit and become entrapped.  The antlion will also use its head to toss sand at any escaping prey, further collapsing the walls of the pit, and bringing the prey sliding down.

The head and jaws of an antlion larvae lurking in its sand pit.

Like other members of the order Neuroptera (such as lacewings), antlion larvae have large, distinctive jaws for hooking their prey.  The moving parts of their jaws form two straw-like tubes through which they can inject digestive chemicals and drink their liquefied prey.  Antlions belong to the family Myrmeleontidae (from the Greek words for “ant” and “lion”).  They take their common (and family) name from the large portion of their diet comprised of ants, but they will prey on anything of an appropriate size which stumbles into their grasp.  Although pit building antlion larvae are the best known (and the most easily spotted) only about 40% of antlion larvae actually build pits.  Other antlion larvae employ a wide variety of hunting strategies.  Some lurk just under the soil and rear up to grab unwary passersby.  Other will even emerge and chase down prey above ground.  (And that is not a creature I would want to see running after me.)

An antlion larvae catching a fire ant in its pit.

Come back next week to see the adult antlion!

Inching Along – Geometridae

An inchworm (family Geometridae) climbs flowers at the Welder Wildlife Refuge, in Texas

Inchworms (also called loopers and spanworms) are a type of caterpillar that take their name from their unique method of moving.  Rather than crawl along leg by leg, these caterpillars have adapted to take advantage of the length of their bodies and “inch” along, contracting the front and back portion of their bodies.  Even the placement of the prolegs (false extra appendages found in some insect larvae) has adapted to this behavior–inchworms lack prolegs in the middle of their body.  Inchworms are typically colored in greens or browns to blend into their environment.  Some, such as the caterpillar below, may have extra filaments to aid in their disguise.  Caterpillars may strike poses to resemble twigs, stems, or even bird poop!

A filament bearing geometrid on a plant stem (Flynn, TX).

The “inchworm” style of movement has independently evolved in several lineages of caterpillars.  However, by far the most abundant and diverse group are the caterpillars of the geometer moths, in the family Geometridae. This family name literally means “earth measurer” and these moths are often better known for their caterpillars than their adults.

Inchworm inching along.

Ants and Hoppers

Carpenter ants tending hopper nymphs in Argentina.

Since we had the spittlebug nymphs earlier this week, I thought I’d take the opportunity to post a picture of some other hopper nymphs.  These little guys are being watched over by several carpenter ant workers, who will collect their sugary excretions and protect them from predators.

A casual observer might confuse these with mealybugs due to their white, somewhat waxy appearance and their location feeding en masse on a plant stem.  (This casual observer would in no way be me.  Nope.)  However mealybugs, like scales, have reduced appendages and secondarily lost wings.  A close look at these guys will reveal not only well developed legs peeking out, but the presence of small, developing wing buds on their backs, indicating that they are late stage nymphs (immature insects).  In fact, that dark shape near the middle left of the mass appears to be an adult thorn-mimicking treehopper, making it likely that these are members of the auchenorrhynchan family Membracidae.

Spittlebugs

Spittlebug nymphs on a plant stem.

Spittlebugs lay their eggs on plant stems.  The young spittlebugs excrete special fluids which they whip into a foamy mass around themselves (in the above image some of this foam has been wiped away).  This ‘spittle’ serves to protect the nymphs from predators as they develop, feeding on plant fluids.  They grow and molt several times (one of the cast off skins can be observed in the above picture), finally leaving the spittle mass after the last molting into their adult form.  Some predatory insects lurk by spittle masses, patiently awaiting the emergence of the insects.  Spittlebugs may live alone or in groups, and the nymphs sometimes leave their own spittle masses to find a new spot or join other spittle masses.

Spittlebugs (family Cercopidae) are in the hemipteran suborder Auchenorrhyncha, and thus are related to leafhoppers, treehoppers, and even cicadas.  The adult insects resemble broad and stout-bodied leafhoppers, and are sometimes called froghoppers due to their somewhat frog-like appearance.

Close up of spittlebugs.

Camping Caterpillars

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.

An opened nest of tent caterpillars.