Drymaplaneta semivitta, a lovable indigenous cockroach commensal in human homes in Perth, Western Australia

In my house and garden in inner-city suburban Perth, Western Australia, I have long had a friendly policy towards weeds and commensals. As far as possible, I allow 'wildlife' to share my living space, even indoors.

I can therefore report, based on at least three decades of experience, on the topic of the indigenous cockroach Drymaplaneta semivitta (https://www.inaturalist.org/taxa/339919-Drymaplaneta-semivitta and https://file.lacounty.gov/SDSInter/acwm/1102012_Gisbornecockroach.pdf).

This species is closely related to Drymaplaneta communis (https://en.wikipedia.org/wiki/Common_shining_cockroach), which inhabits the largest Australian cities, in the southeast of the continent.

Drymaplaneta semivitta is a flightless cockroach with a body about 2.7 cm long. It is smaller-bodied than the non-indigenous, and far more abundant and gregarious, Periplaneta americana (https://www.inaturalist.org/taxa/82231-Periplaneta-americana and https://entnemdept.ufl.edu/creatures/urban/roaches/american_cockroach.htm#:~:text=The%20life%20cycle%20from%20egg,150%20young%20in%20her%20lifetime.) and Blatella germanica (https://www.inaturalist.org/taxa/121237-Blattella-germanica).

It is also slow-moving and confiding, hardly reacting to human approach even in warm weather. It shows the same disarming fearlessness towards the human species as do two indigenous birds common in my garden, namely Rhipidura leucophrys (https://www.inaturalist.org/taxa/8143-Rhipidura-leucophrys) and Grallina cyanoleuca (https://www.inaturalist.org/taxa/8583-Grallina-cyanoleuca).

Drymaplaneta semivitta is remarkably constant as a presence in my house and garden, being encountered as individuals (never in groups) behind wall-murals, in piles of paper, under bark the on trees, and in coarse mulch. It climbs smooth walls easily. It seems naturally scansorial, rather than terrestrial. It lacks defence-postures or -displays, and flees reluctantly/sluggishly.

In my experience, it has shown no noticeable seasonal variation in activity or breeding. This implies slow and steady metabolism, growth, and reproduction.

I have never felt any impulse to kill this species, even in my kitchen. I find its demeanour on discovery, which is confiding, unexcitable, and 'tame', to be endearing. It is silent and seemingly odourless. The only nuisance that I have noticed is the fecal specks that it leaves on the wall behind picture-frames

If one considers both body-size multiplied by the number of individuals per unit area, D. semivitta is the major indigenous invertebrate - and indeed non-human animal of any sort - inhabiting the interior of my house.

The gecko Christinus marmoratus (https://www.inaturalist.org/taxa/33449-Christinus-marmoratus) is commensal in Perth, and is at least three-fold more massive than D. semivitta.

However, it remains at the outside of the building, is relatively scarce (with an average of only a few encounters per year, usually when some object such as a brick-pile is disturbed), and seems never actually to enter my house. The lizard is far more secretive, far less commensal, and far less numerous than the indigenous cockroach.

Publicado el 8 de febrero de 2023 20:34 por milewski milewski


@tonyrebelo @jeremygilmore
Have either of you never observed Deropeltis erythrocephala (https://www.inaturalist.org/taxa/567994-Deropeltis-erythrocephala) inside a building?

Publicado por milewski hace 10 meses

Using https://www.inaturalist.org/observations?locale=en&place_id=113055&preferred_place_id=113055&taxon_id=567994&verifiable=any
and summarizing the habitat field (a voluntary data field) entered via the https://www.inaturalist.org/projects/habitats-s-afr project:

Gardens 63
Fynbos 43
Dwellings 29
Renosterveld 10
Succulent Karoo 10
Albany Thicket 4
Cropland 3
Afrotemperate Forest 2
Plantation 2
Strandveld 2
Grassveld 1
Nama Karoo 1
Savanna: Moist 1
Urban Parkland 1
Wetland 1

Unknown 5
(blank) 311
These should be corrected for the defaults to correct for bias. I dont have data for the range of the species, which is an issue, (and there may well be regional differences, & I have not curated/cleaned the data for 4 years, & does one subsample for animals, invertebrates, insects or roaches, & etc. ) - but overall it is:

Publicado por tonyrebelo hace 10 meses

But compare with Periplaneta americana https://www.inaturalist.org/observations?locale=en&place_id=113055&preferred_place_id=113055&taxon_id=82231&verifiable=any

Dwellings 22
Gardens 15
Urban Parkland 3
Savanna: Moist 2
Afrotemperate Forest 1
Desert 1
Plantation 1
Succulent Karoo 1
Unknown 1
(blank) 95

Publicado por tonyrebelo hace 10 meses

I have only seen Periplaneta americana living in buildings. Occasionally we get Deropeltis erythrocephala in the garden, but usually in Fynbos.

Publicado por jeremygilmore hace 10 meses

@tonyrebelo @jeremygilmore

Many thanks for this valuable information.

I lived in Cape Town for a total of more than 20 years, but I never encountered Deropeltis erythrocephala.

Publicado por milewski hace 10 meses


Many thanks again for contributing to this scrutiny of Deropeltis erythrocephala, which is the South African cockroach most comparable with Drymaplaneta of Australia.

I note the following differences.

a) is larger-bodied than Drymaplaneta,
b) is far more sexually dimorphic,
c) has large wings (males, https://www.inaturalist.org/observations/37451194) whereas Drymaplaneta is wingless,
d) has a defence posture (females seem to straighten their legs, to make themselves look large, and/or show off the reddish hue of the legs, https://www.inaturalist.org/observations/141154207), whereas Drymaplaneta has no defence posture at all,
e) has a subtle form of aposematic colouration (possibly associated with the pre-contact release of noxious odour), whereas there is no aposematic aspect whatsoever to the colouration of Drymaplaneta,
f) carries a proportionately larger ootheca (compare https://www.inaturalist.org/observations/140276194 with https://www.inaturalist.org/observations/142061884), suggesting greater litter-size, and
g) has hardly adopted the interior of human dwellings as habitat, whereas Drymaplaneta has done so to the extent that most of the individuals inside houses may hatch, reside, and senesce within human-occupied rooms.

Publicado por milewski hace 10 meses

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