Halloween Spiders

A bold jumping spider, Phidippus audax

In honor of Halloween I bring you spiders!  This little guy is a bold jumping spider who has been keeping me company in the lab for over a year now.  Bold jumping spiders are some of the largest and most recognizable jumpers I see around here, and some of my favorites.  These spiders are typically black with three white spots on the abdomen, although these markings may be yellow or orange in young spiders.  This particular spider started out with orange markings like a jack-o-lantern face which changed to white after the first molting in the lab.  A closer look will also reveal metallic blue or green chelicerae (mouthparts for grasping food, and the fangs in spiders).

A bold jumping spider, Phidippus audax

Jumping spiders belong to the family Salticidae, from the latin “salto” or “jump”.   As their name suggests they are excellent jumpers, able to leap more than ten times their body length to capture prey or avoid predators.  They do not spin webs, but use their silk as safety lines to anchor them when jumping, and also weave refuges, thick mats of silk to hide and shelter in.  The position and size of the eight eyes is often used as a character to distinguish spiders; the center front pair of eyes in salticids is enlarged, giving them excellent color vision and resolution as well as a somewhat more humanlike appearance than many other spiders.

A bold jumping spider confronting a pair of forceps.

Color Lubbers

An aposematic lubber grasshopper from Argentina (Romaleidae)

Some of my favorite Argentinian insects were these large, colorful lubber grasshoppers.  They were certainly striking, and easy to spot with the aposematic coloration they use to warn predators that they are poisonous.  Lubber grasshoppers belong to the orthopteran family Romaleidae, so named from Greek “romaleos” meaning “strong of body” in reference to their generally large size.  The term “lubber” may also be in reference to the old English use of the word to mean “clumsy” and “stout.”  Many lubber grasshoppers also have shortened wings, especially in the females, as we’ve seen previously, and are poor fliers and slow hoppers due to their heavy bodies.  In the case of this lubber grasshopper, any slowness or clumsiness due to body size is compensated by toxic chemicals that make them distasteful to potential predators.

An aposematic lubber grasshopper in Argentina (Zoniopoda inheringi).

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 Ant Symbiotes – 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.

 

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 in fire ant brood pile.

 

 

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

 

 

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

 

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 from a fire ant nest.

 

Ant Movie

 

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)

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).

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

Tags: Techniques

Hail to the Queens – the polygyne fire ant

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!

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).