Päiväkirja-arkisto kohteelle huhtikuu 2022

1. huhtikuuta 2022

Let's talk Tibellus!

In Minnesota there are three species belonging to the genus Tibellus that are known to occur (and likely occur statewide): T. oblongus, T. maritimus and the rarer T. duttoni. There is also a fourth species that is hypothetical in its occurrence in the state and believed to most likely occur in the northern half: T. asiaticus . They all belong to the family Philodromidae and are commonly called running crab spiders and members of the genus Tibellus are often called the slender running crab spiders. As their name suggests, these spiders are slimmer and very quick on their feet. They do not spin a web like orbweavers but rather are active hunters.

Members of this genus are often found in grassland habitats and that makes them fairly easy to find, especially if you use a net to sweep through the grass. Their coloration and pattern enable them to blend in with stalks of dry grass and they often perch vertically on stems (and hide behind them like a woodpeckers hide behind the trunks of trees).

I have not been able to determine what underlying environmental factors determine which species is likely to occur in a given grassland. I have found that T. maritimus and T. oblongus are most common and sometimes co-occur in the same grassland (though often it is one or the other). I've also found the three common species in a single grassland in south-central Minnesota which was surprising because I would expect competition to limit how many species can occur in a single area since they occupy the same niche.

Identification of these spiders is a little tricky. Most taxonomic keys begin by asking how many pairs of macrosetae (thick hairs) are on the ventral side of the first leg's tibia. Most of Minnesota's species have 3 pairs but T. duttoni has 4 pairs. If the macrosetae are not visible in a picture (more than likely), one could look for a pair of dark spots on the dorsal surface on the rear third of the abdomen. T. maritimus lacks these spots, but the other three species all have them. Most Tibellus with a pair of dark spots on the abdomen are likely T. oblongus due to this species' broad distribution and how commonly it occurs. However, examination of the first leg's tibia or reproductive structures (palp/epigynum) are really necessary in order to rule out the other two species which also show the paired spots.

Happy spidering!

Lähetetty 1. huhtikuuta 2022 19:59 käyttäjältä cheins1 cheins1 | 0 kommenttia | Jätä kommentti