Phasmida

Tilgner (2002)

Introduction

Phasmida are terrestrial, nocturnal, phytophagous insects found in nearly all temperate and tropical ecosystems (Günther, 1953). Scientists have described over 3,000 species (Bragg, 1995), yet this figure is uncertain since some taxon names are synonyms, and many new species have not been formally described.

Characteristics

Phasmida are variable in appearance, ranging from relatively generalized forms, to some that are wonderful mimics of sticks and/or leaves. They display varying degrees of brachyptery, and can be winged or wingless. The tarsi have three articles in Timema Scudder and five in other Phasmida. Cerci are composed of one article, except for adult males of Timema which have a lobe on the right cercus.

Sexual dimorphism is usually extreme: the males are smaller and more gracile than the females. Reproduction is typically sexual, but parthenogenesis occurs frequently. The egg capsule is distinctively shaped, possessing a lid called the operculum and a micropylar plate (Sellick, 1997). Eggs are large and oftentimes highly sculptured resembling plant seeds. They are laid singly, and are dropped, flicked, buried, glued to a surface, or riveted to a leaf. Some species that drop the eggs rely on ants to disperse them in a process analogous to myrmecochory (Windsor et al., 1996). The entire life cycle from egg to adult can take from several months to several years depending on the species.

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Egg capsule of Extatosoma popa. The nymph escapes by popping off the operculum. Photograph copyright © 2001, Erich Tilgner.

Phasmida possess several unique anatomical features that distinguish them from other Neoptera and indicate they are a monophyletic group (see Tilgner et al., 1999; 2002). For example:

• The labrum is emarginated.
• All possess a pair of exocrine glands inside the prothorax (in a few species, these glands can discharge an irritating, tear gas-like spray used for defense).
• The intestine has unique filament bearing glands.
• Thorax fused with abdominal sternum I
• The dorso-ventral muscles of the abdomen are numerous, short, and arranged in parallel.
• Males of many species possess a unique sclerite termed the vomer. This structure is located above the genitalia and permits the male to clasp the female.

Discussion of Phylogenetic Relationships

Timema is hypothesized to be the sister group to the remainder of Phasmida (Kristensen, 1975, Bradler 1999, Tilgner et al. 1999, Tilgner 2002), termed Euphasmida by Bradler (1999). Timema lack the autapomorphies of Euphasmida and possess traits found in other more distantly related Neoptera (Tilgner et al. 1999). 

Other Names for Phasmida

• Phasmatodea
• Phasmids

References

Bradler, S. 1999. The vomer of Timema Scudder, 1895 (Insecta: Phasmatodea) and its significance for phasmatodean phylogeny. Cour. Forschungstinst. Senckenb. 215:43-47.

Bragg, P.E. 1995. The Phasmid Database version 1.5. Phasmid Studies 3(2):41-42.

Günther, K. 1953. Über die taxonomische Gliederung und die geographische Verbreitung der Insektenordnung der Phasmatodea. Beiträge zur Entomol. 3:541-563.

Kristensen, N.P. 1975. Phylogeny of hexapod "orders." A critical review of recent accounts. Z. Zool. Syst. Evol.13:1-44.

Sellick, J.T.C. 1997. Descriptive terminology of the phasmid egg capsule, with an extended key to the phasmid genera based on egg structure. Syst. Entomol. 22:97-122.

Tilgner, E. H., Kiselyova, T. G., and McHugh, J. V. 1999. A morphological study of Timema cristinae Vickery with implications for the phylogenetics of Phasmida. Dtsche. Entomol. Z. 46(2):149-162.

Tilgner, E. H. 2002. Systematics of Phasmida. Ph.D. Dissertation, University of Georgia.

Wheeler, W.C. 1998. Sampling, groundplans, total evidence and the systematics of arthropods, In Fortey, R.A. & Thomas, R. H. (Eds.) Arthropod Relationships, Systematics Association special volume series 55, Chapman and Hall, London.

Windsor, D.M., Trapnell, D.W. and Amat, G. 1996. The egg capitulum of a neotropical walkingstick Calynda bicuspis, induces aboveground egg dispersal by the ponerine ant Ectatomma ruidum. J. Insect Behav. 9:353-362.

Information on the Internet

• Systematics of Phasmida. Full text of Erich Tilgner's Ph. D. Dissertation.