Bug FAQGiant Cactus Longhorn Beetle
Moneilema gigas · Order: Coleoptera · Family: Cerambycidae
The Giant Cactus Longhorn Beetle is a large, black, flightless beetle that lives in the Sonoran Desert below 1500 m elevation. Adults appear in the summer monsoon season and feed on the surface of cholla and prickly-pear cacti, while larvae bore into cactus roots and stems.
Source: Wikipedia
How to recognize it
Its front wings are fused into a single hardened shell and it has a rounded abdomen and thorax with limited wing muscles.
Source: Wikipedia
Size
It is a large beetle.
Source: Wikipedia
Where it lives
It lives in the Sonoran Desert at elevations below 1500 m.
Source: Wikipedia
What it eats
Adults eat the surface of cholla and prickly-pear cacti.
Source: Wikipedia
Life cycle
Larvae develop inside cactus roots and stems, which can kill vulnerable cacti. Adults emerge in mid to late summer during the monsoon season.
Source: Wikipedia
When you see it
They are most active in mid or late summer, coinciding with the monsoon.
Source: Wikipedia
Where it comes from
It is native to the Sonoran Desert region.
Source: Wikipedia
Lookalikes
They resemble and mimic the behavior of stink beetles in the genus Eleodes.
Source: Wikipedia
Where it is found in the US
Recorded in 3 of 51 states and DC. Most records: Arizona, New Mexico, California.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: native in North America; native in United States. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
Questions people ask
What do Giant Cactus Longhorn Beetles eat?
Adults feed on the surface of cholla and prickly-pear cacti, while larvae bore into cactus roots and stems.
Source: Wikipedia
When are they active?
They are most active in mid to late summer during the desert monsoon season.
Source: Wikipedia
What other bugs do they look like?
They mimic the appearance and behavior of stink beetles of the genus Eleodes.
Source: Wikipedia
Same family (Cerambycidae)
House LonghornHylotrupes bajulusCan damage your home
Asian Longhorned BeetleAnoplophora glabripennisDamages trees, gardens or crops
Red Milkweed BeetleTetraopes tetrophthalmus
White-spotted SawyerMonochamus scutellatusCan damage your home
Red Pine Longhorn BeetleStictoleptura rubra
Spotted Longhorn BeetleRutpela maculataSources
- Wikipedia: https://en.wikipedia.org/wiki/Moneilema_gigas
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-24 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-24.