Volume 39, Number 1,
October 1992:
Springtails

Text-only version

ABOUT THIS ISSUE
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IN THIS ISSUE
- part 1
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- part 3
- part 4
- part 5
- part 6
- part 7
- part 8
- part 9
- part 10

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Springtails
by Kenneth Christiansen

As with mice, many species of Collembola appear to be compete with each other. Recent studies have shown that different species interact in at least three different ways to affect each other's population growth: 1) by direct contact, 2) by producing materials onto the ground on which they live which affect other individuals, and 3) by producing chemicals which can be borne through the air which have some affect on other individuals. The most remarkable thing is that the interaction between the species may be very different in the three different types of interaction. For example let us consider the interaction between our old friend Folsomia candida and a member of the family Hypogastruridae, Xenylla grisea (Figure 12). The latter has no effect upon the population growth of the former as the result of direct contact or materials produced on the ground; however it has a positive effect when only airborne chemicals are involved. On the other hand F. candida has a strong negative effect on the population growth of X. grisea in direct contact or production of materials on the ground, but a strong positive effect when only airborne chemicals are involved. Other species have a negative interaction in all three types of situation. This remarkable complexity of interaction has not been examined yet in other animals, so we do not know if it is a peculiar feature of just the Collembola.

We are not certain when the chemicals causing these interactions are nor how the animals affect each other's reproductive rates. However, we do know that there are sometimes hostile interactions between Collembola when food is scarce. In such interactions, the Collembola use their antennae as clubs to beat each other over the heads as shown in Figure 13. In severe fights they run around in a tight circle, beating each other over their rear ends in a kind of dogfight. Remarkably these fights become less frequent and less severe in some species as the animals become more crowded.

Most springtails can only survive, or at least be active, in humidity conditions near the saturation point. Surface life in drier conditions requires physiological adaptations which are not well understood. Most of the species which can remain active in relatively dry conditions have scales or dense hairs which retard water loss. Eggs are generally less sensitive to desiccation than the animals themselves. Eggs and adults of some species shrivel up in dry conditions but can resume development or activity when re-hydrated by rain; such species can exist in sites which are only temporarily moist. Members of some genera such as Folsomides even build "nests" of fecal pellets in which this suspended animation, or anabiosis, occurs. If soil layers do not dry completely, surface species may survive by restricting their activity to night. Some species survive dry hot periods by ecomorphosis - metamorphosing into physiologically inactive form. Such forms usually have vestigial mouthparts, non-functional digestive systems, low metabolic rates and an appearance so strikingly different from the normal stage that some were originally placed in different genera from their normal forms. With the onset of normal conditions they molt again, recovering the normal form and function. One great mystery concerning this phenomenon is that in many species it appears only in the males.