Two quick points.

First, in response to Poly's question, toads certainly can become obese. Adults don't need as much food relative to their size as the rapidly growing juveniles. Fed an excess of high-calorie foods (mice, waxworms, etc.) can result in extremely fat toads which may suffer health problems, including corneal opacities (eye condition, can result in blindness). Transitioning to less-frequent feedings after they are mature and keeping low-fat insects as the staple of their diet is best for the long-term health of your pet.

Second, the size of the prey item is partly a matter of common sense. The "space between the eyes" rule is a good idea for the more "hard-shelled" prey items but I don't believe it should be slavishly adhered to for soft-bodied prey. I think you can bend the rule for silkworms, hornworms, earthworms, etc. As an example, I have an extremely large female Cranwell's horned frog (named Ralph, of course). She might be 1.25 inches between the eyes but she is now pushing 6 inches in length. She can easily eat a dozen or so ~6 inch nightcrawlers or 4 inch hornworms at a feeding. I can't possibly imagine feeding her a hundred or so ~1 inch crickets! GADZOOKS! Ditto for some of my larger toads... I personally have no problem with feeding a 6 inch nightcrawler to my 6 inch frog (or a 1 inch earthworm to a 1 inch frog, if I had one). Just be cautious and use your discretion and common sense...