Crematogaster

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Crematogaster
Crematogaster mormonum (worker)

Crematogaster mormonum (worker)

Systematics
Class : Insects (Insecta)
Order : Hymenoptera (Hymenoptera)
Family : Ants (Formicidae)
Subfamily : Knot ants (Myrmicinae)
Genre : Crematogaster
Scientific name
Crematogaster
Lund , 1831
Worker of Crematogaster mormonum . The tapered abdomen (gaster) is clearly visible at the end.

Crematogaster is a genus of ants (Formicidae) from the subfamily of knot ants (Myrmicinae). The genus is distributed worldwide with over 400 species, especially in the tropics and subtropics, in Central Europe there are three species.

features

As with all representatives of the knot ants, the stalk , i.e. the connection between the mesosoma and the gaster (abdomen) is two-part, the two parts ( petiolus and postpetiolus ) are clearly separated from the gaster. In Crematogaster , the postpetiolus is inserted dorsally on the first gastric segment. The guest end is clear in workers and slightly pointed in female sex animals. The poison glands are strongly regressed. The antennae of the workers usually have 11 segments, only in one line of African and Asian species do they consist of 10 segments. The last two to four segments are thickened like a club. The propodeum shows a pair of thorns dorsally in most species, the workers have no further reinforcement. The workers are of the same size or show a continuous size polymorphism , there is no clearly distinguishable major caste .

distribution and habitat

The genus is distributed worldwide mainly in the tropics and subtropics, three species occur in Central Europe. The tropical species are predominantly tree-dwelling ( arboricol ) and are among the dominant forms of life there. In the subtropics and temperate climates, the nests are mostly in the ground and under stones.

Way of life

Nest locations and nest structure

The genus shows an enormous diversity in terms of way of life and ecological niche. The colonies can be very large and cover entire tree canopies, or they can be very small and located on a single dead branch. Large colonies tend to have numerous interconnected nests. In the Neotropic , the nests are mainly created in dead wood, with the spectrum of possible nest locations ranging from individual twigs to large branches and trunks. Only a few species make their nests here in living branches. In Asia and Africa, large groups of species have adapted very closely to individual or a few plant species and live exclusively on and in these plants, whereas such closely adapted species are rare in the Neotropics.

Many species can make a cardboard-like material from chewed plant fibers, but most species only use this material in relatively small quantities to create closed chambers within the nests or to restrict access to the nest. Some types, e.g. B. Crematogaster stollii in Central America, use it to build tunnel-like galleries on trunks and branches to connect the nests of a colony, each of which is located in the tips of living branches. Other species build exposed cardboard nests that enclose small branches. These free nests can be free from any vegetation, but some species create epiphyte gardens on the nest surfaces . Most tropical species inhabit trees, but a few species build their nests in the leaf litter. These species are mostly nocturnal.

Social structure of the colonies

Most species have only one queen ( monogynous ) in a nest, only a few species have several queens ( polygynous ) in one nest . In some species, females of a so-called intercaste have been found, which morphologically mediates between workers and queens. These females do not take part in the work in the nest, but apparently only lay eggs, which in particular serve as food for the larvae. The intercaste does not have a sperm library and therefore its eggs cannot be fertilized. The eggs are fertile , however ; if they can develop, males will hatch from them. Often nests are found in which only the intercaste, workers, eggs and larvae are present. So far it is unclear whether these are parts of a colony whose nests with queens are elsewhere, or whether these are complete colonies that were founded by inter-box females.

Social behavior

Most species, and especially those that form large colonies with many nests, are aggressive and territorial. When threatened, the workers of most species fold the guests forward over the mesosoma like a scorpion ; the enemy is smeared with a viscous defense secretion released from the gas tip. A few species, such as Crematogaster carinata in Central America , which inhabit large polygynous colonies with many nests, are non-aggressive and inhabit their territory and even their nests together with other species of ants.

nutrition

The species of the genus are probably predominantly omnivorous and eat both vegetable matter such as nectar and animal material. The workers seldom attack active and mobile prey, but often little or completely immobile invertebrates, e.g. B. pupae or larvae attacked by insects. Scouts individually search for food and when they find a food object they recruit additional workers from the colony. Many species care for plant lice (Sternorrhyncha) in order to eat their excrement, which is rich in nutrients (" honeydew ") ( trophobiosis ); the degree of specialization in this food source varies greatly depending on the species.

Systematics

Based on its morphological features, the genus can be clearly defined as a monophylum . Due to the worldwide distribution and the abundance and diversity, especially in the tropics, a large number of species were described, up to 1995 889 first descriptions were available. Almost all of these descriptions were made independently and summarizing revisions have so far only been presented for a few regions, e.g. B. for North America. There have been some attempts to establish sub-genres, but these are not considered to be well founded and are not generally accepted. Overall, according to Longino , the systematics within the Crematogaster genus represents “one of the intractable messes” in the ants systematics.

The list reproduced here with over 400 species follows ITIS:

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Individual evidence

  1. ↑ Summary by John T. Longino: The Crematogaster (Hymenoptera, Formicidae, Myrmicinae) of Costa Rica. Zootaxa 151, 2003: pp. 1–150, here p. 4.
  2. ↑ Species list of the genus Crematogaster at ITIS ( online , accessed on January 12, 2011)

literature

  • John T. Longino: The Crematogaster (Hymenoptera, Formicidae, Myrmicinae) of Costa Rica. Zootaxa 151, 2003: pp. 1–150 ( [1] Online as PDF)
  • Bernhard Seifert: Ants: observe, determine. Naturbuch Verlag, Augsburg 1996. ISBN 3-89440-170-2 : pp. 108 and 238-239

Web links

Commons : Crematogaster  - collection of images, videos and audio files