It goes without questioning when I say that Strumigenys are some of the most diverse ants out there, and their 843 valid, described species can back that statement up. While they may not be as large or as noticeable as some other large ant genera such as Camponotus, Strumigenys in my opinion are far more interesting.
Etymology
The word Strumigenys derives from the Latin term struma, meaning "a glandular swelling," and the Greek word genys, meaning "jaw." This refers to the type species, Strumigenys mandibularis, which has heavy-set, swollen jaws, which does not fit well with most other species. Speaking of fitting well with other species, Strumigenys species have almost no characteristic shared by every species. Most Strumigenys species have a peculiar membranous membrane on the petiole and post-petiole as well as strangely modified hairs throughout the ant's body, though neither of these traits are shared by all members of the genus. Many do have a uniform tan color, but many have more of an orange color, some are brown, some are yellow, and yet others have a panda coloration, with bizarre patterns of black and white throughout. One of the only uniform traits throughout the genus is their small size, many species not extending past 3 millimeters, and their slow movement. However, these two traits can be applied to many other ant genera.
Terminology
Prior to 2007, Strumigenys was separated into two main genera, the snap-jawed Strumigenys, and the toothy, triangular-jawed Pyramica. Before that, Strumigenys was split into dozens of genera, however of the years, Strumigenys absorbed all other genera, though Strumigenys is in need of a revision. It is possible that in the future, old sister genera could be revised, and new genera could be formed.
Biology
Many people have asked me how to find Strumigenys, and I'll tell you, people often make it way more difficult than it really is. Strumigenys are surprisingly common ants, and you don't even have to be lucky to find them. In fact, in my tiny backyard alone, I have uncovered five different colonies of two different species of Strumigenys, and as I have found stray workers in a few different locations, and considering the fact that Strumigenys workers never forage more than a few centimeters away from their nest, there are at least three more nests I've yet to uncover. I've also found four founding queens. My backyard isn't even anything special. It's small, has very few trees, is covered in pine straw, and has only two soil extremes, extremely moist, and very dry. There's really no in-between, except for after it rains.
Strumigenys can be found just about anywhere. While many wedge-headed species prefer undisturbed deciduous woodlands, many other species such as snap-jaws and the invasive Strumigenys membranifera can be found in an urban setting. For example, I've found Strumigenys membranifera workers at a baseball field, a new state record of Strumigenys silvestrii under some tightly packed logs only a few meters away from a street, Strumigenys colonies at pools, and in other bizarre places you wouldn't think to find cryptic ants. You can often find Strumigenys inside of other ant's nests, usually Aphaenogaster or Lasius, but can also be found in nests of Crematogaster, Linepithema, and even coexisting peacefully with other species of Strumigenys. There's even a western US species that makes it's nests exclusively inside the nests of the much larger Trachymyrmex arizonensis, and Strumigenys maynei frequently nests with Platythyrea conradti. The larger ant species don't mind the presence of the tiny Strumigenys, as they help to keep the springtail population in check, which can become quite an annoyance if their numbers are too high.
Strumigenys feed almost exclusively on Collembolans (springtails) and other small soil arthropods, sometimes taking down prey far larger than themselves. The way in which Strumigenys capture their prey varies from species-to-species, but it often involves the ant slowing sneaking up on a resting prey item while slowly sensing it with it's antennae. The ant then moves almost imperceptibly slow towards it's target while holding it's jaws open. It then lunges forward, seizing an appendage or a hair and subdues it with a sting. Some species have take this a step forward and have evolved a snap-jaw mechanism, holding their jaws open at a 90o angle or wider, and slamming their jaws shut at insanely fast speeds on a trigger hair. In any case, Strumigenys are highly efficient predators.
Habitat
There are many ways in which Strumigenys can be found, but almost all species are subterranean, though a few have adapted to an arboreal lifestyle. The subterranean species can sometimes be found under rocks on the forest floor. However, great care must be taken to insure that the ants are not missed. Check for movement, any movement at all. Their small size, slow speed, and cryptic coloration adds up to an ant nearly impossible to spot by the casual observer, so be careful. Often times, the ants are right in front of your face, and careful observation of a minute or more may be required. Strumigenys may also be nesting in old, hollow roots under rocks, or other hollow structures, such as nuts or hollow twigs, or even hollows inside the rocks themselves. Other times however, Strumigenys are not found under any structures in particular. Often times, colonies can be found at the bases of trees under the leaf litter, and it may take a little bit of sifting in order to collect the entire colony (more details below). A good rule of thumb is to search around the nest entrances of other, larger ant species, especially Aphaenogaster. Some Strumigenys spp. colonies are found almost exclusively near (usually within a few centimeters of their nest entrance) or inside of Aphaenogaster spp. nests. One example of this is Strumigenys rostrata which is a large (in Strumigenys terms), dark species from the eastern US. It is found near or inside the nests of Aphaenogaster tennesseensis a species that tends to nest at the bases of trees inside of rotting wood segments. Strumigenys ornata, also from the eastern US, is often found inside of the nests of Aphaenogaster fulva. When found in Aphaenogaster nests, Strumigenys colonies are often found in the kitchen midden chambers, where the most springtails are located, though workers do tend to do quite a bit of foraging through the tunnels and chambers of the nest.
Many Strumigenys species are found nesting inside of rotting wood, usually under the bark, which can be easily pealed up to reveal colonies, which often form 'walls' around the nest, presumably to protect themselves from predators such as beetle larva or other larger ant species. Many species however prefer to nest deeper in the wood, especially if the wood is in a later stage of decomposition, where tunneling can be done easier, though these ants don't tend to create tunnels themselves, rather preferring to take over the abandoned tunnels of termites or beetle larva. These colonies can be easily uncovered by pealing back pieces of rotting wood with a hammer or a painting knife. Something that can be used to hook into the bark and peel pieces back. The key is to be very careful, as these ants are very fragile and can be easily damaged if you drive the edge of a hammer straight through their nest, and the last thing you want to do is to accidentally injure the queen(s). More precise tools may be needed once a colony is uncovered, especially if the colony has extensive tunnels. Usually nothing more than a strong pair of forceps is needed, but a pocket knife could always come in handy.
Arboreal species of Strumigenys are usually restricted to the tropics and species are few and far between. Colonies are often found inside of plant cavities, such as hollow twigs, tunnels from beetles, termites, and other wood-dwelling insects, and under loose bark. Several species of Strumigenys do forage arboreally, such as the common southeastern species Strumigenys louisianae, though these species rarely ascend higher than a few meters, and many are not good climbers as they do not have pads on their feet that help other ant species cling to smooth surfaces such as leaves.
Many terrestrial Strumigenys species nest in old nuts and hollow twigs that have fallen onto the forest floor. Often times, these nuts or twigs are partway to fully buried in the leaf litter. The best way to search for these colonies is to gather up large quantities of nuts or twigs from the forest floor, preferably ones with holes in the (mostly in the case of nuts). Bring these nuts and twigs back to a well-lighted area and carefully crack them open into a container lined with talcum powder, Fluon, or any other slip medium (most species of Strumigenys cannot climb up a smooth surface but other ant species that may be nesting in the nuts or twigs may be able to). As mentioned before, but I will put more emphasis on this statement, be careful! Strumigenys are extremely fragile and sensitive ants, and the last thing you want to do is injure the ants.
One of the best ways to find Strumigenys is to sift for them. Often times little more is needed than two containers of the same size or one smaller than the other (the preferable option). In one of the containers (the smaller one if one is smaller), the bottom needs to be cut out and replaced with a fine mesh, large enough to let ants and other small soil invertebrates through, but small enough that larger soil elements cannot be let in, such as leaves and twigs. Scoop up a handful of leaf litter and place it into the container with the screen, while holding it over the other, non-screened container. Shake the container with the material in it and let the dirt fall through for about thirty seconds, or until all small material is sifted through into the second container. Shake the second contained until all sifted material it flattened out and even. Carefully search through the material and look for Strumigenys moving. If there are a few workers here and there, keep sifting in that same area until the colony is uncovered. This may take several tries. If no workers are found in the collection material, search in other areas, preferably at the bases of trees, which is where many soil-dwelling colonies are located.
Queens
While it's not easy starting off Strumigenys colonies from a single queen, it can be done, though it take patience and may take several tries to get it right. Strumigenys are very sensitive ants when it comes down to it. You need the proper amount of moisture, food, and a dark environment to get them going, but if you're able to provide this, than you can try and raise up a Strumigenys queen.
Strumigenys queens and males (if the species has males) fly from late summer into early to mid-fall during the late afternoon. However, it's far easier to find queens in their claustral cells under rocks and inside of nuts and hollow twigs.
Queens may take a very long time to produce anything, but the key is to try and leave them alone as much as you can. Queens are semi-claustral and eat springtails and other small soil arthropods while founding, so having a small foraging area is probably best for them so they can remain in darkness while being fed. If all goes well, a little over two months after laying her first eggs, you should be welcoming your first, tiny Strumigenys workers.
Materials
There are quite a few materials you will need when Strumigenys hunting. One of the most important tool you could have on hand is a handy aspirator. An aspirator, otherwise known as a pooter, is a tool used to collect ants using suction. Be sure the mesh is fine enough that no ants can get through, and no soil particles can get accidentally inhaled. An aspirator can also be used to count ants collected by placing them into a container and as a single ant is sucked up, you press a button and when all ants are collected, you add up the total and get your number of ants.
Another handy tool is a pair of featherweight forceps. Featherweight forceps are an important collecting tool, and can be used to pick up ant specimens. Never, ever use a pair of hard-tip forceps, as these could easily injure or even kill your ants. The only time hard-tip forceps should ever be used is when moving large soil particles out of the way or when carefully digging through a rotting log.
A killing vial is optional, but can certainly come in handy if you would like a preserved specimen of the ants you are collecting. The killing vial should be filled with ethanol or alcohol, anything that will kill and preserve the ant in a way in which it can be pinned or sent somewhere, or just preserved the way it is.
A Winkler sifter is a tool used for sifting more effectively. A Winkler can be used in many different ways. It can be used as a compact sifting container (mentioned above) in order to sort out larger soil material to be placed into a smaller material for sorting, or it can be used in a different way, placing the contents into a Winkler bag to sit in the sun for a few days while the insects fall into a vial. This vial can be used with or without a killing agent, depending on what your intentions with the ants are. Similarly, a Berlese funnel can be used to sort through material, though less effectively. This method uses a bright overhead light to drive soil invertebrates into a vial below. Both of these methods are fairly expensive, though the Berlese funnel can be less so and can be easily hand-crafted.
It's a good idea to have at least a few extra collection containers on hand. Any size can work, though a nice variation of sizes is always better.
A flashlight can be extremely useful when looking for Strumigenys in dim lighting conditions, including under rocks, inside of tree trunks or hollows, and under unmovable objects, such as fixed tree stumps. Burrows are also good to look into. When anting in a rainforest, it is always a good idea to have a flashlight on hand as very little light penetrates down to the forest floor. Alternatively, a head lamp can be used in order to free up both hands, which can make collection a whole lot easier.
A pocket knife or a multi-tool can have many uses, such as cracking open hollow twigs, cutting objects, or even when digging through rotting logs. You can never go wrong with a pocket knife. Just remember to be very careful when using it. I've messed up with mine a few times, and I've got the scars to prove it.
A hand lens can be very useful when you need to identify ants out in the field before you get them into a lab setting. I use a lens with 40X magnification, and it works very well out in the field when I don't have a microscope on hand.
A container of water and some cotton balls is extremely important, both for yourself and the ants. Strumigenys are extremely hydration-sensitive. If you leave them without water for even a few hours, that's it for them. Soaking a cotton ball and placing it in with the ants in a temporary holding-cell can make sure this doesn't happen.
Keeping In a Laboratory Setup
Strumigenys are relatively easy to care for once you got the right conditions for them. The most important factor to consider is that Strumigenys are extremely moisture sensitive. I'm no stranger to forgetting to water a Strumigenys colony only to find them dead a few hours later. The best substrate for them is hydrostone. This material doesn't mold and can absorb water very well, therefore keeping the ants hydrated for long periods of time. A Petri dish can be used for housing, but you could also use a simple test tube setup for smaller colonies and a wide array of other nests. Some of the nests by Tar Heel Ants would work really well for small ants like these. Strumigenys colonies don't get very big, usually maxing out at only a few hundred, and as such, you don't need anything crazy big for them to nest in. I simply keep mine in small petri dishes, and they do just fine.
Feeding is a pretty straightforward process but can be tricky before you get the hang of it. Strumigenys exclusively eat springtails and other small soil arthropods, sometimes only one specific group of them. It's best to get a colony of springtails going before you get a colony of Strumigenys, so you have plenty of food to feed them. While feeding Strumigenys may be intriguing to some, it may be uncomfortably boring to others. They move so slowly, and when a springtail moves away, nine times out of ten, they don't follow. However, for people with tons of patience, the moment those jaws clamp around a hapless springtail is a moment well waited for.
In Conclusion
If you are a big fan of small, cryptic ants that will blow peoples minds for reasons like, "How did you even see those!?" Or, "I didn't know ants could get that small!" These ants are definitely for you. They may be small, but they're some of the most diverse ants you will ever come across, and for people who like to have super bizarre ants in their collections, look no further than the most bizarre ant of them all, Strumigenys spp.
