By Dr. David Wartinbee, for the Redoubt Reporter
During the past few months I have been sorting through samples I collected last year from a number of streams and lakes. While I am mostly interested in dipteran insects, I frequently come across other aquatic creatures that pique my interest.
Springtails are wingless creatures that rarely get larger than a few millimeters in length. They are often only as long as the letter “i” in this paper. The one in the picture is only 4 millimeters long and is magnified more than 40 times.
Within the taxonomic arena, collembola have recently become somewhat of a football.
Dozens of my invertebrate books clearly place them within the class Insecta, since they look like insects and have six legs. Up until recently, that is all I have ever known them to be.
Now, DNA analysis indicates that they are not closely related to other insects and should be classified differently.
Currently they are being described as hexapods (six-legged arthropods) that belong within the class Entognatha. This new class consists of arthropods with an internal jaw, which differs from insects since they have external jaws. No matter what their proper names, they are quite interesting creatures.
They get their common name, springtails, due to a forklike structure on the underside of their abdomen. This forked furcula is normally held against the abdomen but it can be swung down quickly and will cause the insect to jump 50 to 100 times its length. The springing furcula looks like a split tail in the pictured collembola.
They also have a strange tubular structure under their abdomen. This structure, called a collophore, is the source of its scientific name, meaning “glue tube.” It was believed the primarily role of this collophore was for gluing the creature to a substrate. It is now thought to be primarily used to absorb water, although a couple species actually do attach themselves to a substrate with this structure.
Collembola are considered to be the most abundant arthropod in the world. There are estimates that soil contains about 80,000 individuals per cubic meter. So, when you see one, you usually see a large number of them. Besides being abundant in soils, they are found in virtually every terrestrial habitat known. They are even found along the rocky shores in Antarctica and at elevations above 20,000 feet.
Studies of tropical forest canopies have shown that springtails are very abundant way up in the trees, too. Here in Alaska we can find them in soils quite commonly, as well as along the shores of streams, ponds, lakes, estuary shorelines and temporary puddles.
Collembola seem to feed mostly on fungal hyphae and fine vegetable detritus. Those found near aquatic habitats feed on algae and diatoms, as well as pollen grains on the water surface. Those found on snow are probably feeding on “snow mold” hyphae growing through the snow, or on detrital particles trapped on the surface.
In some situations springtails can be an agricultural pest, but just as often they are beneficial since they feed on fungal growths that are plant pathogens.
There are some blogs on the Internet that claim these creatures cause terrible rashes and other infections when they supposedly feed on human skin. I have not found any credible sources indicating these claims to be valid, and it seems more like a serious case of mistaken identity.
When collembola are spotted, they will seem to be bouncing around so they are easily misidentified as small fleas. Remember, their mouthparts are internal and are not really suited for feeding on human skin.
The only concern that may be correct is the body hairs of some collembolla might stimulate an allergic reaction in some individuals.
Their overwintering eggs are hatching right now and we can start looking for them along the water edges or under moist detritus.
The young collembola will remain in moist places as they feed and grow. While they do not show much in the way of gender-specific characteristics, they do frequently molt. It has been noted that they might molt more than 50 times during their lifetime.
These unique and really small arthropods are very abundant in Alaska, but you’ll have to make the effort to find them. If you are going to see them, you’ll have to join me on my hands and knees and keep a sharp eye.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Cook Inlet watershed.