oil beetle

US /ˈɔɪl ˌbiː.təl/
UK /ˈɔɪl ˌbiː.təl/
"oil beetle" picture
1.

a beetle of a genus (Meloe) that has a soft, swollen abdomen from which it can exude an oily, acrid fluid when disturbed.

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The children were warned not to touch the oil beetle due to its defensive fluid.
The distinctive black color and soft body are characteristics of an oil beetle.