sapeli, 25.4.2007 20:16:
Itse asiassa, luin äskettäin Tieteen Kuvalehdestä (tms. vastaavasta) että kastemadot pystyvät ihan hyvin selviämään veden alla - syy siihen miksi ne tulee sateella esiin on se, että ne on erittäin herkkiä UV-säteilylle ja käyttää sateista säätä hyväkseen siirtyäkseen paikasta toiseen. Oli mulle ainakin ihan uutinen, olin kans luullu et ne hukkuu...
Niin, tuosta onkin monia teorioita olemassa. Se, että ne hukkuu on yksi, joskin tavallisin. Selvää on ainakin se, että ne eivät selviä veden alla jos sataa vaikkapa monta päivää. Kastemadot kun kuitenkin happea jossain vaiheessa tarvitsevat.
One often sees earthworms come to the surface in large numbers after a rainstorm. There are four theories for this behavior.
The first is that the waterlogged soil has insufficient oxygen for the worms, therefore, earthworms come to the surface to get the oxygen they need and breathe more easily. However, earthworms can survive underwater for several hours if there is oxygen in it, so this theory is rejected by some.
Secondly, some species (notably Lumbricus terrestris) come to the surface to mate. This behavior is, however, limited to a few species.
Thirdly,the worms may be using the moist conditions on the surface to travel more quickly than they can underground, thus colonizing new areas more quickly. Since the relative humidity is higher during and after rain, they do not become dehydrated. This is a dangerous activity in the daytime, since earthworms die quickly when exposed to direct sunlight with its strong UV content, and are more vulnerable to predators such as birds.
The fourth theory is that as there are many other organisms in the ground as well and they respirate as any animal does; the carbon dioxide produced dissolves into the rainwater; it forms carbonic acid and the soil becomes too acidic for the worms and they come seek neutral nourishment on the surface.
Tuossa mainitaan myös UV-säteily yhtenä teoriana.
http://en.wikipedia.org/wiki/Earthworm
