indicator paper

Attach strips (or several) of pH indicator paper (the kind that runs from approx.

(A) Spray pattern on indicator paper elicited by pinching a beetle's left midleg with forceps.

Universal indicator paper is made from absorbent paper that has been impregnated with universal indicator.

To cause the latter beetles to exhaust their secretion, they were held by hand over indicator paper and pinched with forceps until they ceased to respond by spraying.