diff --git a/scrapy/spider/models.py b/scrapy/spider/models.py
index 9210464a3..a9b64995e 100644
--- a/scrapy/spider/models.py
+++ b/scrapy/spider/models.py
@@ -14,32 +14,14 @@ from scrapy.utils.trackref import object_ref
 def _valid_domain_name(obj):
     """Check the domain name specified is valid"""
     if not obj.domain_name:
-        raise ValueError("A site domain name is required")
-
-def _valid_download_delay(obj):
-    """Check the download delay is valid, if specified"""
-    delay = getattr(obj, 'download_delay', 0)
-    if not type(delay) in (int, long, float):
-        raise ValueError("download_delay must be numeric")
-    if float(delay) < 0.0:
-        raise ValueError("download_delay must be positive")
+        raise ValueError("Spider 'domain_name' attribute is required")
 
 class ISpider(Interface, IPlugin) :
     """Interface to be implemented by site-specific web spiders"""
 
-    domain_name = Attribute(
-         """The domain name of the site to be scraped.""")
-
-    download_delay = Attribute(
-         """Optional delay in seconds to wait between web page downloads.
-         Note that this delay does not apply to image downloads.
-         A delay of less than a second can be specified.""")
-
-    user_agent = Attribute(
-         """Optional User-Agent to use for this domain""")
+    domain_name = Attribute("The domain name of the site to be scraped.")
 
     invariant(_valid_domain_name)
-    invariant(_valid_download_delay)
 
 class BaseSpider(object_ref):
     """Base class for scrapy spiders. All spiders must inherit from this