Genus Timema

Timema Scudder, 1895

Scudder coined the name Timema for his "genus nova" in 1895, referring parenthetically to the Greek spelling τίμημα (see 2nd paragraph from the bottom in the original text here).

From the meaning given here for τιμημα, it's not clear what motivated the choice of name for these walking sticks...though Scudder's Latin alphabet transliteration, Timema, means "timid" in Esparanto (see here).

[Note: Gender agreement was incorrect in the forms (i.e. spellings) of the epithets for 5 Timema species when they were originally published. BugGuide uses the emended forms...see here.]

21 spp.(1), of which 20 in our area(2).

There are also at least two more known but undescribed taxa...one using Limber Pine (Pinus flexilis) as host plant; and one using Sargent Cypress (Hesperocyparis sargentii) as host plant.

Body length: Males: 11-20 mm ; Females: 14-28 mm

The species distribution map below (see under "Range"), and the host plant list below (see under "Food" ), can help narrow ID possibilities (though neither are necessarily complete or entirely accurate).

But dependable species ID requires study of the shape of externally visible structures of the terminalia, especially of the male (for non-parthenogenetic spp.)...in conjunction with location, host plant, color and markings.

Note to photo contributors: ID will be facilitated by providing detailed images of terminalia (dorsal view for males; dorsal, ventral, and lateral for females), as well as full-body dorsal views indicating overall color pattern and markings.

             

Males have asymmetric terminalia with two variously lobed cerci ("claspers"), and a more-or-less ribbon-like projection between them (positioned next to the right cercus and called the "intradextral process"). Figures appear here. Keys refer to left and right cerci using the latin terms "sinistral" and "dextral", respectively.

   

Female terminalia are symmetric ... with somewhat longer, more linear, roughly-cylindrical and ridged cerci.

   

A useful one-page visual summary of diagnostic diagrams for terminalia for all 21 currently described species appears in the post thumbnailed below::

   

An online key adapted from Vickery (1993) can be found here...but it covers only 12 species, omitting the 9 species described after 1993 (and, of course, those still undescribed).

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A remarkable aspect of Timema is the existence of a number of parthenogenetic species consisting (at least mostly) of asexually reproducing females.

In bisexual species, adults (as opposed to immature instars or "nymphs") are usually seen paired rather than alone...due to the prevalence of "mate guarding" behavior, in which adult males ride on the backs of adult (or near adult) females for long periods (from hours up to several days). Males are noticeably smaller than females in body size. A rule of thumb given in Sandoval & Vickery (1996) is that a field observation of 5 or more adult females with no males present is a likely indicator of an asexual species.

To each asexual species, there corresponds a closely related sexual species in which the females of the two are visually indistinguishable. These species pairings are as follows:

      T. genevievae and T. podura;

      T. tahoe and T. bartmani;

      T. douglasi and T. poppense;

      T. shepardi and T. californicum;

      T. monikense and T. cristinae (or T. chumash?)

sw. US and Mexico...primarily in CA, but also in far sw. OR, far s. NV, AZ, and Baja California.

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Note that the range map below is not exact and should be cross-referenced with the map of point records here, as well as collection records from the literature.

In particular, the map below under-represents distributions of some species. For instance:

      1) T. californicum has records north of San Francisco Bay in Marin Co.;

      2) T. douglasi and T. poppense are recorded from south of San Francisco Bay in the Santa Cruz Mnts;

      3) T. genevievae has records from areas of eastern Lake and Napa counties; and also from San Benito County.

      4) T. chumash is known from the western San Gabriel Mnts, substantially to the northwest of the area mapped for it.

  So use the map from Wikipedia below as a helpful but rough guide only!

                    Map from Wikipedia, based on map from pg. 1473 of Law & Crespi (2002)

On foliage, twigs, or branches of host shrubs or trees...or on the ground near base of host or other plants, where they may retreat during the day or drop upon disturbance. Sometimes also found sheltering under stones. Host plants mostly associated with chaparral; some with woodlands or forest (e.g. douglas fir, redwood).

Green morphs tend to rest on leaves; brown to gray morphs on stems, branches or ground.

Unstriped morphs are usually associated with broad-leaved host plants (e.g. oaks, ceanothus, manzanita, etc.). Striped morphs are usually associated with host plants having needle-like leaves (e.g. chamise, douglas fir, redwood, etc.).

Coloration, stripes, and other markings serve as camouflage, and are adaptations driven by selection pressure due to predation by visually-oriented birds and lizards. For interesting details, see Sandoval (1994), Sandoval & Crespi (2008), and this course handout & worksheet.

Timema typically feed on leaves at night and rest by day on leaves or stems of their host plants. The following list gives known hosts for each species:

  T. bartmani: white fir (Abies concolor)

  T. boharti: manzanita (Arctostaphylos spp.), ceanothus (Ceanothus spp.), chamise (Adenostoma fasciculatum), oak (Quercus spp.)

  T. californicum: manzanita (Arctostaphylos spp.), ceanothus (Ceanothus spp.), oak (Quercus spp.), mountain mahogony (Cercocarpus spp.), toyon (Heteromeles arbutifolia)

  T. chumash: ceanothus (Ceanothus spp.), oak (Quercus spp.), mountain mahogony (Cercocarpus spp.)

  T. coffmani: juniper (Juniperus spp.)

  T. cristinae: ceanothus (Ceanothus spp.), chamise (Adenostoma fasciculatum), toyon (Heteromeles arbutifolia)

  T. dorotheae: ceanothus (Ceanothus spp.)

  T. douglasi: douglas fir (Pseudotsuga menziesii)

  T. genevievae: chamise (Adenostoma fasciculatum)

  T. knulli: coast redwood (Sequoia sempervirens), ceanothus (Ceanothus spp.)

  T. landelsense: manzanita (Arctostaphylos spp.)

  T. monikense: ceanothus (Ceanothus spp.), mountain mahogony (Cercocarpus spp.)

  T. morongense: wild buckwheat (Eriogonum spp.)

  T. nakipa: manzanita (Arctostaphylos spp.), ceanothus (Ceanothus spp.), chamise (Adenostoma fasciculatum)

  T. nevadense: pinyon pine (Pinus monophylla); juniper (Juniperus spp.)

  T. petita: ceanothus (Ceanothus spp.)

  T. podura: chamise (Adenostoma fasciculatum), ceanothus (Ceanothus spp.), oak (Quercus spp.), mountain mahogony (Cercocarpus spp.)

  T. poppense: douglas fir (Pseudotsuga menziesii), coast redwood (Sequoia sempervirens)

  T. ritense: juniper (Juniperus spp.)

  T. shepardi: manzanita (Arctostaphylos spp.)

  T. tahoe: white fir (Abies concolor)

In most species, eggs are dropped from branches of host plants.

In all species, during egg-laying, females defecate previously-ingested soil, and then use their cerci to firmly cover and pack the eggs with the soil. It's hypothesized this may prevent desiccation, reduce parasitism by micro-hymenoptera, and perhaps provide some protection from fire, which is common in chaparral habitats where Timema are found. Moreover, soil is found in the gut of all newly hatched larvae and Sandoval has observed that laboratory-hatched eggs of all species survived only when provided with soil from their native locality in the first few days after hatching. It is thought that the soil provides offspring access to microbial symbionts for digestion of host plant foliage. Sandoval states that soil ingestion may also reduce toxicity effects from host plant secondary compounds on the larvae.

Parasitism by tachnid flies has been observed for the larvae of T. douglasi, T. cristinae, and T. californicum.

Timema is a genus of small, stout, wingless walking sticks. It is so distinctive that it is the only genus in the entire suborder Timematodea, and it is an ancient group which is phylogenetically basal to the rest of the walking stick order Phasmida. (See Tree of Life website and illustrated cladogram here ).

A fascinating aspect of Timema is the existence of five parthenogenetic species consisting of asexually reproducing females. These are: T. douglasi, T. genevievae, T. monikense, T. shepardi, and T. tahoe. Populations of these species consist (almost) entirely of females (some anomalous males have been observed & collected in T. monikenesis and T. shepardi). Eggs laid by field collected females of these species hatch in the lab to females, which in turn lay eggs without mating that again yield females. In recent years researchers have concluded that some of these species (e.g. T. genevievae) have been asexually reproducing for over a million years. In general, most of the parthenogenetic species have a more northerly distribution than their corresponding sexual species. Various hypotheses have been explored to explain this , e.g. positing dispersal advantages for parthenogens.

T. genevievae, described by Rentz in 1978, was the first Timema species recognized as parthenogenetic. Rentz noted that while other species known at the time emitted an acrid odor, T. genevievae did not. David Weissman suggested that the acrid odor may be associated with mating-related pheromones, which might be unnecessary...and thus lost...in a long-time asexual species. (Vickery 1993, pg. 678).

The history of discovery and description for Timema species is interesting. The first species described, T. californicum, was from a collection in the Santa Cruz Mountains of California in 1895. The second, T. chumash, was described from Los Angeles in 1920 by Hebard, who opined that the genus constituted the most "aberrant" group within the walking sticks. By 1966 seven species had been described from California and adjacent areas of southern Nevada and central Arizona. In 1978 the first parthenogenetic (= all female, asexually reproducing) species was described from southeast of the San Francisco Bay (T. genevievae). Between 1993 and 2001, thirteen more species were described, four of which are parthenogenetic. More known species currently await description, and others likely await discovery.

D. Arbuthnott, M. G. Elliot, M. A. McPeek, & B. J. Crespi (2010). Divergent patterns of diversification in courtship and genitalic characters of Timema walking-sticks. J. Evolution Biol. 23(7) 1399:1411 (PDF)

Bartman, G. & Brock, P. D. (1995). Observations of the appearance and behavior of species of the stick-insect genus Timema Scudder (Phasmida: Timematodea). Bulletin of the Amateur Entomologist's Society, 54:197-203 (Full Text & photos)

Burrows, Malcolm (2008). Jumping in a wingless stick insect, Timema chumash (Phasmatodea, Timematodea, Timematidae). Jour. Experimental Biol. 211: 1021-1028 (Full Text)

Hebard, M. (1920) The genus Timema Scudder, with the description of a new species, (Orthoptera, Phasmidae, Timeminae). Entomological News, 31 126-132 (Read at BHL)

Hebard, M. (1937) Studies in Orthoptera [...]:Notes and a new species of Timema [...]. T. Amer. Entomol. Soc, 63 (3), pp. 347-350. (Read online)

Law, J. H. & B. J. Crespi (2002). The evolution of geographic parthenogenesis in Timema walking-sticks. Molecular Ecology 11: 1471–1489 (PDF)

Maderspacher, Florian (2011). Asexuality: The Insects that Stick With It. Current Biology, 21 (13) pp. 495-497 (Read online here)

Rentz, D. C. F. (1978). A new parthenogenetic Timema from California. Pan-Pacific Entomologist, 54 (3): 173-177. (Full Text)

Sandoval, C.P. (1994). Differential visual predation on morphs of Timema cristinae (Phasmatodea, Timemidae) and its consequences for host range. Biol. J. Linn. Soc., 52, pp 341-356.

Sandoval, C. P. and Nosil, P. (2005). Counteracting selective regimes and host preference evolution in ecotypes of two species of walking-sticks. Evolution 59:2405-2413 (Full Text)

Sandoval, C.P. and Vickery, V.R. (1996). Timema douglasi (Phasmatoptera:Timematodea), a new parthenogenetic species from southwestern Oregon and northern California, with notes on other species. Can. Entomol. 128:79-84.

Sandoval, C. & B. J. Crespi (2008). Adaptive evolution of cryptic coloration: the shape of host plants and dorsal stripes in Timema walking-sticks. Biol. J. Linn. Soc., 94, pp 1-5 (PDF)

Schwander T., Crespi B.J. (2009). Multiple direct transitions from sexual reproduction to apomictic parthenogenesis in Timema stick insects. Evolution 63, 84-103. (PDF)

Schwander T. , H. Lee, B.J. Crespi (2011). Molecular evidence for ancient asexuality in Timema stick insects. Curr. Biol., 21, pp. 1129–1134 (Full Text)

Schwander T., D. Arbuthnott, R. Gries, G. Gries, P. Nosil, & B. Crespi (2013). Hydrocarbon divergence and reproductive isolation in Timema stick insects. Evolutionary Biology 13:151 (Full Text)

Strohecker, H. F. (1966). New Timema from Nevada and Arizona. Pan-Pacific Entomologist, 42 (1) pp. 25-26. (Full Text)

Tinkham, E. R. (1942). A new californian species of Timema (Phasmodea: Timemidae) with zoogeographical notes. Bull. S. Calif. Acad. Sci. 41(2):72-79. pl. 14 (Read at BHL)

Vickery, V. R. (1993). Revision of Timema Scudder (Phasmatoptera: Timematodea) including three new species. Can. Entomol. 125:657–692.

Vickery, V. R. & Sandoval, C. P. (1997). Timema bartmani (Phasmatoptera: Timematodea: Timematidae), a new species from southern California. The Canadian Entomologist 129:933-936

Vickery, V. R. & Sandoval, C. P. (1998). Timema monikensis, Species Nov. (Phasmatoptera: Timemmatidea: Timematidae), a new parthenogenetic species in California. Lyman Entomological Museum and Research Laboratory, Note Number 22.

Vickery V. R. & C. P. Sandoval (1999a). Two new species of Timema, One Parthenogenetic in California. J. Orthoptera Res. 8 (1) 45:47 (JSTOR)

Vickery V. R. & C. P. Sandoval (1999b). Timema coffmani (Phasmatoptera: Timematodea) a New Species from Arizona and Description of the Female of Timema ritensis. J. Orthoptera Res. 8 (1) 49:52 (JSTOR)

Vickery V. R. & C. P. Sandoval (2001). Description of three new species of Timema and Notes on Three Other Species. J. Orthoptera Res. 10 (1) 53:61 (Full Text or PDF)

NEWS ITEM (3/29/18): The Timema Discovery Project is a new initiative aiming to harness as many people as possible to collect much-needed data for advancing our understanding of Timema...please visit the web site, spread the word, and participate!

Wikipedia entry for Timema. An excellent summary.

iNaturalist: List of all iNat Timema posts.

Article from Smithsonian on Cristina Sandoval's research with T. cristinae, and the light it sheds on the process of speciation.

Cristina Sandoval's Timema web page : Images of 13 species, research project info, and bibliography...with some articles available as PDF's. [Archived version, original link defunct]

Patrik Nosil's Timema web page: Info on Timema research projects, excellent color ink drawing by Rosa Ribas showing 25 color forms within 10 Timema species; extensive publications list with many freely available PDF's.

Tanja Schwander's Timema web page: Color drawings of 8 species, interactive map with numerous records of most species, research project info, and bibliography...with some articles available as PDF's. [Archived version, original link defunct]

Timema page from Phasmida species file online, by P.D. Brock.

Timema images from CalPhotos, including images of the parthenogens T. douglasi, T. genevievae, and T. tahoe.

Image of T. dorothea from Hualapai Mnts, AZ. (Source: Tree Of Life web site)

Images of T. poppense: male (right cercus damaged, intradextral process missing?) and another male.