Chrysochus cobaltinus
In 3 days ~50% in a week ~80%
Chrysochus cobaltinus, the cobalt milkweed beetle or blue milkweed beetle, is a member of the diverse family of leaf beetles, Chrysomelidae. It is named after its cobalt-blue exoskeleton, which makes it easy to spot and distinguish, and its tendency to feed off milkweed plants. It occurs in the Western United States and British Columbia.
These beetles use dogbane and milkweed plant species as their primary source of food. Both these plants contain toxic molecules known as cardenolides. C. cobaltinus beetles are resistant to cardenolide toxic effects and can further use them for their own protection against predators. By storing them in pronotal and elytra glands, they can utilize these toxins to their advantage and evolutionary benefit.
These beetles participate in polygamous matings in which both female and male beetles mate with multiple partners. Females can particularly mate with three male beetles simultaneously. After the mating has occurred, males tend to stay mounted on the female's back for an average of 1.7 hours. This postcopulatory behavior has been attributed to increase the male's chance of producing his offspring with his paternal genes. It has been shown to prevent females from mating with other males (while the original male remains on her back) until the male removes himself.
C. cobaltinus beetles have also been shown to partake in hybrid mating between its species and C. auratus (a sister species). In hybrid zones, both beetles live in close proximity which has led to introgression between these two species. Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Yosemite National Park | 🇺🇸 United States |
More parks will be added in future updates.
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Salt Lake City | 🇺🇸 United States | |
| 2 | Sacramento | 🇺🇸 United States |
Possible
About 20% of wildlife watchers report a Cobalt Milkweed Beetle sighting in Yosemite National Park on a given day, based on 126 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 7th most-seen of the 227 insects we can rate there. Over three days the chance rises to about 50%, and over a week to about 80%, if each day is a fresh chance.
July
In that month about 40% of wildlife watchers report a Cobalt Milkweed Beetle in Yosemite National Park on a given day, against under 5% in November to April, the lowest months. That is one of Yosemite National Park's driest months, with about 25 mm of rain against 220 mm in January.
Between 3 and 6 pm
Across all the parks we cover, that three-hour window holds the most Cobalt Milkweed Beetle sightings with a recorded time, and about 8 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
Only Yosemite National Park, in our data
Yosemite National Park is the only park on Wallace's Line with enough records to rate Cobalt Milkweed Beetle sightings: about 20% of wildlife watchers there report one on a given day.
GBIF citizen-science records
It is estimated from how often the Cobalt Milkweed Beetle is recorded against all the insects logged in Yosemite National Park (126 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
