Opiliones in Belgium - About the species
(published VIII.2004)

Our most common species

Rilaena triangularis is present in more than half of the squares from which we have samples (93 out of 170) and is therefore the most widespread Opilionid in Belgium. Two thirds of our captures are juveniles. The species gives us a clear example of the limits of our pitfall samples. Were it not of the juveniles R. triangularis would seem much less common. The adult migrates to higher regions in the vegetation and therefore is less likely to stumble into our traps.
The season of maturity is quite early from March to July - R. triangularis shares this characteristic with Amilenus aurantiacus which also becomes adult in March. Most other species mature in late summer and autumn.

Oligolophus tridens comes next and occurs in 71 squares.

Nemastoma bimaculatum and N. lugubre follow far behind in number of UTM-squares (58 each) but are in fact more numerous than the previous widespread species. N. bimaculatum occurs in 34 % of the squares, and stands for 15 % (n=4947) of all records, while R. triangularis is found in 55 % of the squares with only 10 % (n=3343) of all finds. Both Nemastoma species are often present at the same site, but our maps reveal that N. bimaculatum gravitates more to the west and that N. lugubre is a bit more common in the east.

Paroligolophus agrestis is also present in 58 squares (with 1974 records) and is followed (or preceded, depending on which numbers you consider more important) by Lophopilio palpinalis living in 57 UTM-squares (2637 finds).

Less common, but not considered rare

Species in this group are found in a considerable number of squares or occur in high numbers, but not both. We have finds of Leiobunum rotundum in 55 squares (that is almost as widespread as our more common species) but we have only 749 animals, which is much less. Homalenotus quadridentatus at the other hand is found 2057 times, but only in 32 squares (that is less than 20 % of all sampled UTM-squares). Other species in this class are Phalangium opilio (51 squares), Mitopus morio, Lacinius ephippiatus, Leiobunum blackwalli, Trogulus nepaeformis, Paranemastoma quadripunctatum and finally Opilio saxatilis (23 squares).

Not common, perhaps to be considered rare

I've already explained (Introduction to the maps.) that some of the species probably only seem to be rare because of our sampling methods. This is presumably not the case with species like Mitostoma chrysomelas, Anelasmocephalus cambridgei, Trogulus tricarinatus and Odiellus spinosus which live on the ground layer and occur in only 21, 20, 12 and 3 squares respectively.

Species like Opilio canestrinii and Dicranopalpus ramosus to the contrary, don't turn up in pitfalls and are probably much more widespread than we know at the moment.

The least common harvestmen in our region are Amilenus aurantiacus, Lacinius horridus and Platybunus pinetorum which were found in one single square each (and in the case of P. pinetorum: only once). Perhaps that we can dig them up at some other sites in the southern part of the country, but I don't expect to find them in the northern half.

Path: Opiliones in Belgium