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Stick insects named after Groningen biologist Laas Pijnacker

04 February 2010

A new genus of stick insects has been named after retired University of Groningen biologist Laas Pijnacker – the  Pijnackeria.

The Italian biologist Prof. Valerio Scali has revised the biological classification of stick insects found on the Iberian peninsula. In the Italian Journal of Zoology, he writes that a number of species have been misclassified and actually constitute a group of their own. He decided to name the new group after his colleague Dr Laas Pijnacker, from Paterswolde, with whom he often collaborated in the past.

Dozens of species

Stick insects are insects that look like twigs and are related to grasshoppers. Most stick insects live in the tropics. In Europe, some ten species can be found in the Mediterranean region, but there are none in the Netherlands. Most species are small (up to 10 cm) but there are also very large ones –  the largest known insect is a stick insect found on Papua New Guinea measuring 30 cm.


Stick insects are very popular with children and at petting zoos and other zoos because they’re easy to breed on ivy or brambles. They tickle the imagination with their fantastic type of camouflage. Yet that very characteristic makes stick insects rather boring pets, according to Laas Pijnacker. ‘You don’t hear them and you don’t see them.’ For Pijnacker, the various ways in which they reproduce is of particular interest. Pijnacker is considered an authority the world over on the biology of stick insect reproduction, in particular the cell genetics.


Pijnacker described how stick insects can reproduce parthenogenetically (without fertilization; only females). Chromosome numbers are halved when ova are formed, but double before or afterwards in various ways so the new stick insect ends up with the same number of chromosomes as the parent. Some species are diploid (with two sets of chromosomes like humans) but there are also polyploid species (with three or four sets of all chromosomes). Large numbers of the rare males of a polyploid species were obtained by breeding them on winter and summer varieties of kale.

The dangers of trapping

Valerio Scali is an evolutionary biologist and geneticist at the University of Bologna in Italy, specializing in the stick insects from the Mediterranean region. Scali has spent a great deal of time trapping stick insects. ‘It’s not without its dangers’, he says, ‘to wander around with a flashlight at night through residential and business areas, going through the bushes. I’ve often been chased by vicious dogs and over-enthusiastic cops.’

Scali investigates which species exist and how they are related to one another. To this end, he uses classical methods such as determining the number of chromosomes and their shape but combines these with modern DNA techniques. He has worked closely with Laas Pijnacker since 1968.

Two separate genera

Scali now divides the stick insect genus Leptynia, which consisted of the species Leptynia attennuata and Leptynia hispanica, into two separate genera – Leptynia hispanica is now known as Pijnackeria hispanica. The species differ in morphology in the adult stage as well as in the morphology of the eggs, and also in the number of chromosomes. The new Pijnackeria genus consists as of yet of six species. They can be found on the southern coast of France and on the eastern coast of Spain. Pijnackeria hispanica is the most well known species, but there are also four new species that need to be further described for science. Their preliminary names are Pijnackeria A through D.

Marvellous honour

‘Professor Scali has now made good on a promise made on the occasion of Laas Pijnacker’s retirement eleven years ago’, says University of Groningen evolutionary biologist Leo Beukeboom. ‘Newly discovered species are often named after people, but it hardly ever happens that a whole new genus is designated. It’s a marvellous honour in my book, to have an animal genus named after you. It’s a token of appreciation for a life spent working away at clarifying the reproductive biology of an appealing group of insects.’

Note for the press

More information:
- Prof. Leo Beukeboom, 050-363 8448, e-mail: l.w.beukeboom
- about stick insects: Linda van Zomeren, L.M.van.Zomeren

Original article
Scali, V. (2009). Revision of the Iberian stick insect genus Leptynia Pantel and description of the new genus Pijnackeria. Italian Journal of Zoology, 1748-5851, Volume 76, Issue 4, Pages 381 – 391Valerio

Last modified:24 August 2021 08.45 a.m.
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