Tag Archives: Solenopsis invicta

Ant Bridge

8 Jul
A raft of flooded out fire ants (Solenopsis invicta) forms gradually form a path across the water.

A raft of flooded out fire ants gradually form a path across the water.

A few weeks ago we had a big downpour after a long dry spell.  A&M’s an old campus and doesn’t drain well, so a number of sidewalks and fields were temporarily flooded.  Walking along one of these sidewalks I spotted a fire ant colony that had flooded out into three large rafts of stranded ants.  This rafting behavior is a natural adaptation of fire ants to survive flooding, wherein the workers form a living floatation device to preserve their fellow workers, brood, and queens.

Flooded fire ants (Solenopsis invicta) form a living bridge to dry land.

Flooded fire ants form a living bridge across the water to dry land.

I went home to get my camera, and by the time I returned that afternoon, the rafts of fire ants had managed something I haven’t seen before.  They had spread out and connected up to form a living bridge across the water to dry land.  Ants ran back and forth along a path composed of their living sisters, while those at the surface of the water tested the area ahead with their antennae.  On land a trail of ants was busily moving brood into the dry refuge of a light pole.

An elite pest control agent battles a tentacle of sentient ants with a laser (Source: The Hive).

The reaching trails of ants called to mind a sci-fi/horror film wherein a sentient supercolony of ants formed huge hovering tentacles to drag the humans’ boat to shore.  The pest control people had lasers.  It was a pretty awesome film.  Actually, if you haven’t seen the movie The Hive I highly recommend it, if only for the bizarre plot and ridiculous pseudo-science.   Also, the best movie quote ever:

“We are NOT going to negotiate with ANTS.”

Fictional movies aside, reality is pretty impressive all on it’s own.  I took a whole bunch of pictures of the bridging fire ants, as seen below.  I took some video, too, so hopefully I’ll get that posted when I get the chance to edit something together.

Close up of rafting fire ants in a flooded field.

Forking trail of floating fire ants.

Two isolated rafts of fire ants converge to form a bridge to dry land.

Close up: A floating aft of fire ants bridges a flooded field.

A living raft of fire ants bridges a flooded field. To the right, an alate is visible traversing the bridge to safety.

Related posts:

Queen Ants – Founding a new colony

15 Apr
Camponotus foundress queen tending eggs.

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 disturbed camponotus queen guards her clutch of eggs.

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.

Queen fire ant (Solenopsis invicta) burrowed into cotton with her first brood.

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.

Fire ant queen (Solenopsis invicta) tending brood.

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.

Queen fire ant (Solenopsis invicta) with brood and minims.

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.

A crematogaster queen with brood pile, nurses, and newly eclosed workers.

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 Ant Symbiotes – Martineziana dutertrei

18 Oct


Fire Ant Symbiote, Martineziana dutertrei

A fire ant symbiote, Martineziana dutertrei, with host species.


Here’s another cohabitant I frequently turn up in fire ant nests.  These tiny black beetles belong to one of the largest and most diverse beetle families, Scarabaeidae, the scarab beetles.  They fool their ant hosts by coating themselves in chemicals that cause them to smell and taste like ants.  When I went to research more information on these interesting little beetles I could find very few scientific studies addressing them.  These beetles, Martineziana dutertrei, seem to function primarily as parasites of the ant colonies that host them, stealing prey and other nutrients, and even eating ant larvae.


An ectosymbiotic scarab beetle with a member of its fire ant host species.

An ectosymbiotic scarab beetle with a member of its fire ant host species.


Martineziana dutertrei was apparently introduced to the United States at some point during the introduction of its host species, either the red imported fire ant, Solenopsis invicta, or the black imported fire ant, Solenopsis richteri.  This beetle species are now also found in the nests of a native relative of the infamous imported fire ants, the tropical fire ant Solenopsis geminata, where the beetles have evidently somewhat displaced their own native relative.


A myrmecophilous scarab beetle with its fire ant host species.

A myrmecophilous scarab beetle with its fire ant host species.



A myrmecophilous scarab beetle in fire ant brood pile.

A myrmecophilous scarab beetle in fire ant brood pile.



A fire ant symbiote, Martineziana dutertrei

A fire ant symbiote, Martineziana dutertrei, with host species.



Aphodiine Scarab Beetle - Martineziana dutertrei

Aphodiine Scarab Beetle - Martineziana dutertrei



Aphodiine Scarab Beetle - Martineziana dutertrei

Aphodiine Scarab Beetle - Martineziana dutertrei


Reference: Wojcik, et al.  Ins. Soc. 38:273-281 (1991)

Fire Ant Symbiotes – Nicoletiid Silverfish

15 Oct


Ectosymbiotic nicoletiid silverfish with fire ant host

An ectosymbiotic nicoletiid silverfish with fire ant host species.


The small, pale insect in the midst of the fire ants above is a myrmecophilous (“ant-loving”) silverfish, a member of the order Thysanura and the family Nicoletiidae.  This species of silverfish is one of a small but diverse group of insects and other arthropods that have adapted to living as symbiotes within an ant colony.  Although these insects appear very different to human eyes, they coat themselves in chemicals which fool ants senses of smell and taste into believing them to be nestmates.   Species of myrmecophilous silverfish have been known to groom their ant hosts, and feed on stolen prey or regurgitated food from the ants.

Most people are more familiar with silverfish as the small, silvery insects which frequently inhabit bathrooms or basements in human households.  Silverfish are a primitively wingless species of insect (branching off from other insects prior to the evolution of wings).  Thysanura means “fringe tail” and refers to the three caudal filaments extending in a fringe from the end of their abdomens.  Nicoletiids are generally extremely small and pale, as well as completely eyeless.


A myrmecophilous nicoletiid silverfish.

A myrmecophilous nicoletiid silverfish from a fire ant nest.


Ant Movie

11 Oct


A mountain of exposed fire ants, mounded up on the brood pile to conserve moisture.

A mountain of exposed fire ants, mounded up on the brood pile to conserve moisture.


Okay, last fire ant post for a while .  (Next I’ll do things that live with ants!)  Here’s a video I put together a little while back showing some of my lab work with fire ants.  In particular, you can see the drip floatation technique, which I discussed in my last post, as well as the set up for an experiment on arboreal foraging behavior (climbing), and just a little bit of an experiment that involved using a fluorescent dye to track how collected food is fed to the brood.

Techniques: Drip Floatation Method (Fire ants)

8 Oct
Fire ants (Solenopsis invicta) form a raft after the drip floatation method is employed.

Fire ants form a raft on the rising water after the drip floatation method is employed.

New page up in the techniques section.  Please check out my run-down on the drip floatation method for fire ants.

Although the mounds of fire ants are the most visible part of their home, this structure is used only for regulating the temperature of ants and brood during certain seasons and parts of the day.  A large portion of the nest is hidden from view underground.  The subterranean nesting habits of ant colonies can make the transition from field to lab studies tricky– how does one go about separating thousand and thousands of ants and their delicate brood from a heap of dirt?

In fire ants, the drip floatation method takes advantage of a flood-survival adaptation of the ants to accomplish this task (Banks et al, 1981).

Find more techniques for insect collecting and rearing in the techniques section.


Hail to the Queens – the polygyne fire ant

4 Oct
Multiple queens from a polygyne fire ant colony (Solenopsis invicta).

Multiple queens from a polygyne fire ant colony (Solenopsis invicta).

Different species of ants employ a variety of social strategies.  As I have mentioned in previous posts, some species of ants form vast colonies of millions of workers, while others maintain smaller social structures of only a few hundred ants (or even less!).  Queens of some species mate singly, while others mate multiply, allowing them to produce half-sibling workers from multiple ‘patrilines’and increase the genetic diversity of the colony.  Although colonies of social insects are most famously known for a s ingle reproductive queen (monogyne colonies), a number of species of ants have multiple queens in each colony (polygyne colonies).

Fire ants are an interesting example to consider.  In their native South American range they are strictly monogyne, and extremely territorial and aggressive towards other fire ants.  However, the fire ants introduced into the United States developed multiple queens sometime during the course of their introduction, and polygyne colonies of fire ants make up the majority of the US population.  Queen numbers can range from a few to hundreds of queens, and fire ants may even accept unrelated queens into the colony.  The acceptance of multiple queens also corresponds to a decrease in aggressiveness and territoriality towards other polygyne fire ant colonies.  This has been suggested as a contributor to the rapid spread of fire ants across the southern US.

Fire ants!

1 Oct
A fire ant worker (Solenopsis invicta) in a laboratory foraging experiment.

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 (Solenopsis invicta) swarms in response to a disturbance to the mound.

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 (Solenopsis invicta).

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 (Solenopsis invicta).

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 fire ants and brood (Solenopsis invicta).

Polymorphic worker ants and brood (Solenopsis invicta).

Pit Monsters – The Immature Antlion

27 Aug
Antlion Larvae (Myrmeleontidae)

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.

An antlion larvae (Myrmeleontidae) in sand pit.

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.)

Antlion larvae (Myrmeleontidae) with fire ant (Solenopsis invicta).

An antlion larvae catching a fire ant in its pit.

Come back next week to see the adult antlion!