Then there's the thirty-six-year-old San Diego woman who, in 1977, plotted to kill her twenty-three-year-old Marine drill instructor husband for his $20,000 insurance policy. She dropped the venom sac from a tarantula in a blackberry pie she baked, but he only ate a few bites. Next she tried electrocuting him in the shower, but that too failed. So did attempts to kill him with lye, run him down in a car, inject an air bubble into his veins, and slip amphetamines in his beer while driving in hopes he would hallucinate and crash.
Exasperated, she enlisted a twenty-six-year-old female companion in crime. Together, they beat the husband over the head with metal weights as he slept. It was only at that point that he finally succumbed (unverified).
Source