Monday, November 24, 2014

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).

Thursday, November 20, 2014

Lakin Grasshopper

Grasshopper species diversity in the southwest U.S. presents enough of a challenge for the amateur naturalist, but then you have the Lakin Grasshopper, Melanoplus lakinus, that can apparently pass for several hundred species all by itself. That's an exaggeration, of course, but there is such great variability in the color, pattern, and wing length of this species that it is mind-boggling.

Lakin Grasshopper male

Lakin Grasshopper is often overwhelmingly abundant in disturbed habitats such as vacant lots and weedy fields and rangeland filled with its favorite host plants, members of the goosefoot family Chenopodiaceae. This includes Russianthistle ("tumbleweed"), kochia, and native saltbush (Atriplex spp.). It will also feed on various forbs and grasses such as lambsquarters, western wheatgrass, and downy brome. Despite high population densities in some years, it is seldom a crop pest.

Lakin Grasshopper female

This is a grasshopper of the Rockies and Great Plains, ranging from South Dakota and southern Minnesota south through western Iowa, most of Kansas, western Oklahoma, the west half of Texas, plus Nebraska, Colorado, New Mexico, and the eastern two-thirds of Wyoming, Utah, and Arizona. It also occurs deep into central Mexico.

Red form female from New Mexico

Melanoplus lakinus is a pretty "average" grasshopper. Adult males measure about 22 millimeters in body length, females 30 millimeters. Most specimens are short-winged as adults, but some are fully-winged. The overall color varies greatly from brownish or gray to green or even red. The tibia ("shin") segment of the hind leg is usually blue, armed with spines that are black or at least black-tipped. The inner surface of the hind femur ("thigh") is often reddish in part, especially along the bottom edge where the tibia folds into it. The top surface of the femur is most often marked with pronounced dark bands.

Green form female from Colorado

Dark bands on the abdomen, especially near the base, are helpful in recognizing the species in the field, but ultimately one has to examine the external genitalia of the male to confirm identification.

Ok, so how do you even tell apart the different genders? Below is an image that shows the male and female side-by-side, from the rear. The male is on the right. The female is on the left, but her abdomen is twisted to repel his advances, or accept his overtures, I'm honestly not sure which because I did not stick around long enough to see the outcome.

Male on right, female on left, rear view

The male's parts are pretty complicated, but you want to look at the shape of each "cercus," paired tail-like appendages. In the example below, we see that the cercus of M. lakinus is shaped something like a Hershey's candy kiss: broad at the base and tapered toward the tip. Next, take a look at the shape of the subgenital plate. It is best to view it directly from the rear, like in the image above. We can see it has a low, blunt tooth right in the middle. The supra-anal plate also offers species-specific details, but they are more difficult to discern, especially in images.

Anatomy of male M. lakinus

When two grasshoppers do get together, it looks like this:

Mating pair, male on top

Pretty kinky, almost literally! Mated females deposit clusters of eggs ("pods") in the soil by telescoping their abdomen as deep as it can reach. The eggs are held together by a kind of foamy secretion that hardens to protect the mass from environmental extremes. The eggs hatch in late May or early June, on average, the following year. In Arizona, where summer monsoons trigger hatching, emergence is usually in early July. The nymphs pass through five instars (an instar is the interval between molts), reaching adulthood in about a month.

Long-winged female from New Mexico

This year was a good one for the Lakin Grasshopper here in Colorado, and also in New Mexico, as heavy spring rains provided the nymphs with plenty of food after years of draught. The adults have hung around a long time, too. Just yesterday I spotted one basking on the sunny side of a building in our townhouse complex.

Sources: Capinera, John L. , Ralph D. Scott, and Thomas J. Walker. 2004. Field Guide to Grasshoppers, Katydids, and Crickets of the United States. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 249 pp.
Branson, David H. and Bethany Redlin (eds.). 2004. Grasshoppers: Their Biology, Identification and Management. 2nd Edition. US Department of Agriculture, Agricultural Research Service.
Grasshoppers of Colorado

Sunday, November 16, 2014

Ballooning Spiders

Do you remember that meme that went around on Facebook expressing gratitude that spiders can't fly? Here it is:

Well, not so fast my friends. Spiders actually can get aloft, thanks to the phenomenon of "ballooning."

Ballooning is the number one way that spiders disperse themselves across the landscape. It is practiced mostly by immature spiders that do not weigh much and are easily blown away; but many spiders are quite small as adults, too, and they can balloon as well. It is a way spiders avoid competition with each other for prey and "web sites."

This technique is brilliantly simple. The spider simply climbs to the top of a vertical object like a plant stalk, fencepost, or mailbox, and issues threads of silk from its spinnerets. When the spider detects a breeze, it stands on "tiptoe," facing the wind, and tilts its abdomen toward the sky. With any luck, the air currents whisk the spider off its perch and up, up, and away it goes.

Ballooning wolf spider, Blue Stem Prairie Open Space

Recent investigations also suggest that spiders can harness electrostatic forces in the atmosphere to balloon on calm days and/or achieve greater success than they might from the wind alone. This is beyond both my grasp of physics and the scope of this post, but you are welcome to read more here.

The spider families that utilize ballooning the most include the crab spiders (Thomisidae), orbweavers (Araneidae), long-jawed orbweavers (Tetragnathidae), and dwarf spiders (subfamily Erigoninae of the Linyphiidae). Personally, I have also seen wolf spiders (Lycosidae) ballooning, like this one at Bluestem Prairie Open Space along the edge of Johnson Reservoir near Colorado Springs, on March 10, 2014.

Alex Harman also documented a ballooning event of immature Six-spotted Fishing Spiders, Dolomedes triton, at Horicon Marsh in Wisconsin on October 26 of this year.

© Alex Harman

Ballooning is most often performed in spring and late fall by spiderlings, but adult dwarf spiders balloon during the winter, too. The most favorable conditions for a "launch" are when the weather changes to warm days after a prolonged period of cold. This creates updrafts as the ground temperature heats rapidly. Here on the Front Range of Colorado, gusts can be strong and spiders are no doubt carried a long distance.

Darwin, during his voyage on the H.M.S. Beagle, noted large numbers of ballooning spiders coming to rest on the ship's rigging. At the time, the vessel was approximately 100 kilometers off the eastern coast of South America, and Darwin suspected the spiders had drifted at least that distance, if not farther.

Not only are ballooning spiders transported horizontally, they can be blown to high altitudes as well. At least one spider has been collected by airplane at 15,000 feet over Tallulah, Louisiana during a study that lasted from 1926-1931 (Glick, 1939). The greatest number of specimens was still taken at well under 1,000 feet, however.

Gossamer, © Fairyist.com

"Gossamer" is the term for the silk lines spiders create when ballooning, and the cumulative effect can literally shroud the landscape in a blanket of gossamer as the spiders come to rest. Considering that there are easily dozens upon dozens of spiderlings per egg sac, multiplied by dozens of egg sacs, multiplied yet again by however many species exist in a given area, it is no wonder that ballooning individuals can create such a spectacle of spent silk.

Not every attempt at aerial navigation is a success, of course. I personally witnessed a small crab spider take off from a utility box in my neighborhood, only to land unceremoniously about three feet away in the street.

Ballooning crab spider, Xysticus sp., Colorado Springs

Still, spiders are able to achieve amazing feats this way. They are often among the first animals to colonize islands, and habitats destroyed by storms, volcanoes, and other natural disasters. Re-colonization of the island of Krakatau, and the blast zone around Mount St. Helens, are two of many well-documented instances of ballooning spiders conquering new territories.

Sources: Brunetta, Leslie, and Catherine L. Craig. 2010. Spider Silk. New Haven, Connecticut: Yale University Press. 229 pp.
Foelix, Rainer. 2011. Biology of Spiders (Third Ed.). Oxford: Oxford University Press. 419 pp.
Glick, P.A. 1939. The Distribution of Insects, Spiders, and Mites in the Air. Washington, DC: United States Department of Agriculture Technical Bulletin No. 673. 151 pp.

Friday, November 14, 2014

Thank you, followers!

I can think of no better way to use my 500th post than to thank the many people who read this blog faithfully. Without followers like you, I never would have reached this milestone. Many days I have wondered why I bother posting, but then I look at the growing number of icons under "members" in the right sidebar, and remember who is waiting for the next story.

We ♡ our followers!

Friends who are more tech-savvy than myself also remind me that there are hundreds of other people looking in that don't show as members. Every month or so I also get a report from Google that surprises me with how many "hits" this page receives daily, and where those hits are coming from. Sure, most of my audience is from the U.S. and Canada, but I also have visitors from the United Kingdom, Australia, and South Africa. I may need to make some field trips abroad so I can talk about arthropods from those places, too.

Last month I had over 9,000 new visitors, 274 returning visitors. Facebook and Blogger are my top "social sources" by far, with WordPress, reddit, and Twitter bringing up the rear. That surprises me because I get re-tweeted all the time (and thank you for that!).

My overall goal is to reach an audience unfamiliar with insects and arachnids, providing the most accurate and relevant information I can. I also want to encourage other naturalists to keep on finding and observing invertebrates, reporting their own sightings, images, videos, and audio recordings to appropriate archives. I welcome suggestions for how to improve on that.

It is important to note that many of my posts could not be possible without input from entomologists and arachnologists far more expert than myself. I frequently need to have specimens identified before I can write about the species, genus, or family, and were it not for specialists willing to share their knowledge, I would be nowhere.

Lastly, if you have an enterprise that has anything to do with a positive approach to natural history, have written a book, or do public programs, I would be willing to put up an advertisement for you, as I have done with BioQuip. Don't be shy, I am always delighted to reward good work, and would happily devote a blog post to your business, achievements, or observations, especially if you do not have a blog of your own.

Thank you again for making "Bug Eric" a successful venture. I look forward to continuing to produce it for as long as I can. There is certainly no shortage of subject matter, even if I had started several lifetimes ago. Oh, wait, the internet has not even existed for that long.