You can verify if a web crawler accessing your server really is PetalBot.
1. Run a reverse DNS lookup on the accessing IP address from your logs, using the host command.
2. Verify that the domain name is in aspiegel.com.
3. Run a forward DNS lookup on the domain name retrieved in step 1 using the host command on the retrieved domain name. Verify that it is the same as the original accessing IP address from your logs.
$ host 126.96.36.199
188.8.131.52.in-addr.arpa domain name pointer petalbot-114-119-160-240.aspiegel.com
$ host petalbot-114-119-160-240.aspiegel.com
petalbot-114-119-160-240.aspiegel.com has address 184.108.40.206