Springtails

Imagine animated flecks of salt and pepper running, even jumping, all over the bathtub, shower stall, wash basin, or window sill. Maybe you don't have to imagine, maybe you have actually experienced this and thought you were seeing things. Welcome to the world of springtails, tiny invertebrates that are among the most plentiful of organisms, both indoors and out.

Classification

So primitive, in the evolutionary sense, are springtails that scientists cannot even agree whether they are insects. They used to be, as members of the order Collembola. These days they are more likely to literally be placed in a class by themselves: the class Collembola; and treated as "non-insect hexapods." Regardless, there is no denying their importance as members of the soil fauna, and instrumental in the recycling of nutrients there.

Size and Abundance

Springtails are very small. Most are 1-3 millimeters. A "giant" sprigtail may measure 6 millimeters. The largest known species reaches a maximum of 17 millimeters. What they lack in size they more than make up for in sheer numbers. Estimates of the number of springtails per cubic decimeter of (forest) soil vary from 200 to 1,800, probably according to soil texture, composition, and fertility. A decimeter, by the way, is one-tenth of a meter (Bellinger, et al., 2014).

Many springtails active at night on a porch

Habitat

The Collembola are not always restricted to soil and leaf litter. Some species inhabit caves, others inside rodent burrows, still others occupying intertidal zones. Some species live in ant or termite nests, still others on the surface of still waters, even the surface of the snow, hence the common name of "snow fleas" for Hypogastrura nivicola and its relatives. You probably have springtails in the potting soil of your houseplants, and around the drains of sinks, tubs, and basins. The one overriding prerequisite for the presence of springtails is the presence of moisture.

Food

Springtails feed on all manner of organic matter, but the majority seem to eat rotting plants, insect frass (poop), fungal hyphae and/or spores, pollen grains, or dead invertebrates. A few are predatory on soil micro-organisms like rotifers and tardigrades ("water bears"), while fewer still are predatory on other springtails and tiny insects. They cannot be considered pests, but could, in rare instances, be indicative of mold or fungal issues when found indoors.

Look closely: Many springtails from under a board in a field

Anatomy

Not all springtails....spring. Still, they get their common name from two peculiar appendages that most springtails possess. A forked, tail-like appendage called the furcula on the ventral (underside) of the abdomen projects forward from near the tip of the abdomen on its fourth or fifth segment. When "cocked," the fercula (aka furca or furculum) hooks into a latch-like organ called the tentaculum (or "retinaculum"), located on the third abdominal segment. When the tentaculum releases, the furcula is driven downward against the substrate (surface on which the animal is resting), catapulting the springtail up and away, often several times the creature's body length. This bouncing locomotion is certainly observable by the naked eye.

All springtails feature a "ventral tube" or collophore, on the underside of the first abdominal segment. It's function is poorly understood, but it has been suggested that it may act as an extra leg, helping the creature navigate slick surfaces by means of adhesion; it may also function as a grooming organ, and/or as an intake for liquid water.

Lastly, springtails can be identified by having the tibia and tarsus fused into a "tibio-tarsus;" by the simple eyes composed of up to eight ocelli; four- to six-segmented antennae; and mouthparts concealed by folds in the cuticle of the animal's face.

A large and ornate springtail from beside a stream

Life Cycle

The sex life of springtails is not terribly intimate. Males produce packets called spermatophores that contain sperm. He may make a direct deposit to the female's genital opening, but most species deposit spermatophores one at a time on the surface of the substrate. Sometimes the spermatophore is on a hair-like stalk. There are apparently a variety of strategies for improving the odds that a female will find and pick up the species-appropriate spermatophore in a timely fashion. Males will actively consume old spermatophores, so time is of the essence.

A mated female will lay eggs individually or in small clusters in the soil. The babies that hatch resemble miniature versions of the adults, and thus go through "simple" or "incomplete" metamorphosis, molting several times after emerging from the egg.

Interestingly, the adults continue molting, up to fifty times during their mature lifespan. This may be due to the fact that springtails absorb oxygen directly through their soft exoskeleton. Chinks in the armor may not facilitate proper metabolic processes.

Controlling indoor springtails

At worst, springtails should be considered a cosmetic nuisance, and certainly not worthy of chemical assaults. They are not considered a risk to human health, the health of pets, or destructive to property. If you must, here are some steps you can take to literally dry them to death, the only sure-fire "cure."

• Do not overwater houseplants. Should you find springtails in houseplants, take the plants outside and allow the soil to dry out for several days.
• Consider using a dehumidifier in the room where you are seeing springtail activity. Lowering the atmospheric moisture level is always helpful in minimizing or eliminating springtail populations.
• Spread a very thin layer of diatomaceous earth (DE) where you are seeing springtails, such as on a window sill. Reconsider this if you have curious pets or toddlers, as DE is essentially pulverized glass. Diatomaceous earth etches the cuticle of insects, causing them to dehydrate and die.
• Repair worn weatherstripping on doors, and seal cracks and crevices that springtails (and other arthropods) could crawl through to get indoors.
• Inspect firewood, toys, and any other objects brought indoors from outside. This is essential for preventing all potential pests from entering the home.

Sources: Bellinger, P.E., Christiansen, K.A., and Janssens, F. 1996-2014. Checklist of the Collembola of the World.
Berenbaum, May R. 1989. Ninety-nine Gnats, Nits, and Nibblers. Urbana: University of Illinois Press. 263 pp.
Hopkin, Steve. 2014. Collembola Photo Gallery.
Hopkin, Stephen. "The Biology of the Collembola (Springtails): The Most Abundant Insects in the World," The Natural History Museum (UK).